Một lớp có 30 học sinh gồm 12 học sinh nữ

Trường hợp 1: Chọn 3 nữ, 2 nam ⇒ có

 cách chọn

Trường hợp 2: Chọn 4 nữ, 1 nam có 

 cách chọn

Do đó có

 cách chọn.

Chọn B.

Một lớp có 30 học sinh gồm 12 học sinh nam, 18 học sinh nữ, cần chọn ra 5 học sinh gồm cả nam và nữ đi thi giới thiệu sách. Hỏi có bao nhiêu cách chọn để trong đó có ít nhất 3 nữ?

A.

A. 53856

B.

B. 90576

C.

C. 28800

D.

D. 14400

Đáp án và lời giải

Đáp án:B

Lời giải:

Chọn đáp án B

Trường hợp 1: Chọn 3 nữ, 2 nam ⇒ có

cách chọn Trường hợp 2: Chọn 4 nữ, 1 nam có cách chọn Do đó có cách chọn.

Đáp án đúng là B

Câu hỏi thuộc đề thi sau. Bạn có muốn thi thử?

Bài tập trắc nghiệm 60 phút Bài toán về tổ hợp - TỔ HỢP VÀ XÁC SUẤT - Toán Học 11 - Đề số 63

Làm bài

Chia sẻ

Một số câu hỏi khác cùng bài thi.

• Tìm số hạng không chứa

  trong khai triển
  biết
  .

• Trong khai triển nhị thức Niu-tơn của

  có bao nhiêu số hạng?

• Số các tập con của một tập hợp gồm

  phần tử là:

• Cho đa giác đều

  có
  đỉnh. Người ta lập một tứ giác có
  đỉnh là
  đỉnh của
  . Tính số tứ giác được lập thành mà không có cạnh nào là cạnh của
  .

• Cho đa giác đều có

  cạnh
  . Tìm
  để đa giác có số đường chéo bằng số cạnh?

• Cho

  đường thẳng phân biệt đồng quy tại
  trong đó không có ba đường thẳng nào cùng nằm trên một mặt phẳng. Có bao nhiêu mặt phẳng đi qua
  trong số
  đường thẳng nói trên?

• Nhân dịp lễ sơ kết học kì I, để thưởng cho ba học sinh có thành tích tốt nhất lớp cô An đã mua

  cuốn sách khác nhau và chọn ngẫu nhiên ra
  cuốn để phát thưởng cho
  học sinh đó mỗi học sinh nhận
  cuốn. Hỏi cô An có bao nhiêu cách phát thưởng.

• Giả sử ta dùng

  màu để tô màu cho
  nước khác nhau trên bản đồ và không có màu nào được dùng hai lần. Số các cách để chọn những màu cần dùng là:

• Cho tập hợp

  có
  phần tử. Số tập con gồm hai phần từ của
  là

• Một lớp có 30 học sinh gồm 12 học sinh nam, 18 học sinh nữ, cần chọn ra 5 học sinh gồm cả nam và nữ đi thi giới thiệu sách. Hỏi có bao nhiêu cách chọn để trong đó có ít nhất 3 nữ?

• Trong một buổi khiêu vũ có

  nam và
  nữ. Hỏi có bao nhiêu cách chọn ra một đôi nam nữ để khiêu vũ?

• Tìm số hạng chứa

  trong khai triển

• Hệ số của số hạng chứa

  trong khai triển của biểu thức
  với
  bằng:

• Một đa giác lồi có

  đỉnh. Chọn ngẫu nhiên ba đỉnh của đa giác lồi và nối chúng lại với nhau ta được một tam giác. Tính xác suất để tam giác thu được có ba cạnh là ba đường chéo của đa giác đã cho.

• Trong khai triển nhị thức

  xét các khẳng định sau: I. Gồm có 7 số hạng. II. Số hạng thứ 2 là 6x. III. Hệ số của
  là 5. Trong các khẳng định trên:

• Giả sử rằng, trong Đại hội thể dục thể thao tỉnh Gia Lai năm

  có
  đội bóng đăng ký tham gia giải, được chia thành
  bảng
  ,
  ,
  ,
  , mỗi bảng gồm
  đội. Cách thức thi đấu như sau: Vòng
  : Các đội trong mỗi bảng thi đấu vòng tròn một lượt, tính điểm và chọn ra đội nhất của mỗi bảng. Vòng
  (bán kết): Đội nhất bảng
  gặp đội nhất bảng
  ; Đội nhất bảng
  gặp đội nhất bảng
  . Vòng
  (chung kết): Tranh giải ba: Hai đội thua trong bán kết; tranh giải nhất: Hai đội thắng trong bán kết. Biết rằng tất cả các trận đấu đều diễn ra trên sân vận động Pleiku vào các ngày liên tiếp, mỗi ngày
  trận. Hỏi Ban tổ chức cần mượn sân vận động trong bao nhiêu ngày?

• Cho các số nguyên dương

  ,
  . Mệnh đề nào sau đây sai?

• Một hộp đựng 5 viên bi màu xanh, 7 viên bi màu vàng. Có bao nhiêu cách lấy ra 6 viên bi bất kỳ?

• Khai triển

  . Tính tổng
  .

• Cho tập

  có
  phần tử. Biết rằng số tập con có
  phần tử của
  bằng hai lần số tập con có
  phần tử của
  . Hỏi
  thuộc đoạn nào dưới đây?

• Hệ số của

  trong khai triển biểu thức
  bằng

• Tổng

  bằng

• Hệ số của số hạng chứa

  trong khai triển nhị thức
  (với
  ) là :

• Một trường cấp 3 của tỉnh Đồng Tháp có 8 giáo viên Toán gồm 3 nữ và 5 nam, giáo viên Vật lý thì gồm 4 giáo viên nam. Hỏi có bao nhiêu cách chọn ra một đoàn thanh tra công tác ôn thi THPTQG gồm 3 người có đủ 2 môn Toán và Vật lý và phải có giáo viên nam và giáo viên nữ trong đoàn.

• Tìm hệ số của

  trong khai triển
  .

• Đội văn nghệ của nhà trường gồm

  học sinh lớp 12A,
  học sinh lớp 12B và
  học sinh lớp 12C.Chọn ngẫu nhiên
  học sinh từ đội văn nghệ để biễu diễn trong lễ bế giảng. Hỏi có bao nhiêu cách chọn sao cho lớp nào cũng có học sinh được chọn?

• Cho số nguyên dương

  , tính tổng
  .

• Số tự nhiên

  thỏa
  thì:

• Với

  là số nguyên dương thỏa mãn
  , hệ số của số hạng chứa
  trong khai triển
  bằng

• Tìmsốhạngtổngquát ( chứa

  ) trongkhaitriển
  .

• Cho

  là số nguyên dương thỏa mãn
  . Hệ số của số hạng chứa
  của khai triển biểu thức
  bằng:

• Cho tập

  có
  phần tử. Tìm số tập con có
  phần tử của tập
  .

• Hệ số của số hạng chứa

  trong khai triển nhị thức
  (với
  ) là :

• Tìm số nguyên dương

  thỏa mãn
  .

• Cho khai triển

  và các hệ số thỏa mãn
  . Hệ số lớn nhất là

• Cho các phát biểu sau: a) Quy tắc cộng chỉ có thể áp dụng cho hai tập hợp

  và
  . b) Khi sắp xếp
  phần tử của tập hợp
  với
  theo một thứ tự, ta được một hoán vị các phần tử của tập
  c) Số hoán vị của một tập hợp có
  phần tử là
  d) Khi lấy
  phần tử của tập hợp
  có
  phần tử và sắp xếp chúng theo một thứ tự ta được tổ hợp chập
  của
  phần tử của
  e) Số các tổ hợp chập
  của một tập hợp có
  phần tử với
  là
  . f) Ta quy ước
  và
  với
  . Số các phát biểu sai trong các phát biểu trên là:

• Cho tập hợp

  có
  phần tử
  . Biết rằng số tập con của
  có
  phần tử nhiều gấp
  lần số tập con của
  có
  phần tử. Hãy tìm
  sao cho số tập con gồm
  phần tử của
  là nhiều nhất.

• Lập sốcó 9 chữsố, mỗi chữsốthuộc thuộc tập hợp 1,2,3,4 trong đó chữsố4 có mặt 4 lần, chữsố3 có mặt 3 lần, các chữsốcòn lại có mặt đúng một lần. Sốcác sốlập được là

• Tìm số nguyên dương

  thỏa mãn
  .

• Số hạng thứ 3 trong khai triển

  không chứa x. Tìm x biết rằng số hạng này bằng số hạng thứ hai của khai triển
  .

Một số câu hỏi khác có thể bạn quan tâm.

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  The changing profile of a city in the United States is apparent in the shifting definitions used by the United States Bureau of the Census. In 1870 the census officially distinguished the nation’s “urban” from its “rural” population for the first time. “Urban population” was defined as persons living in towns of 8,000 inhabitants or more. But after 1900 it meant persons living in incorporated places having 2,500 or more inhabitants.

  Then, in 1950 the Census Bureau radically changed its definition of urban to take account of the new vagueness of city boundaries. In addition to persons living in incorporated units of 2,500 or more, the census now included those who lived in unincorporated units of that size, and also all persons living in the densely settled urban fringe, including both incorporated and unincorporated areas located around cities of 50,000 inhabitants or more. Each such unit, conceived as an integrated economic and social unit with a large population nucleus, was named a Standard Metropolitan Statistical Area (SMSA).

  Each SMSA would contain at least (a) one central city with 50,000 inhabitants or more or (b) two cities having shared boundaries and constituting, for general economic and social purposes, a single community with a combined population of at least 50,000, the smaller of which must have a population of at least 15,000. Such an area would include the county in which the central city was located, and adjacent counties that were found to be metropolitan in character and economically and socially integrated with the county of the central city.By 1970, about two-thirds of the population of the United States was living in these urbanized areas, and of that figure more than half were living outside the central cities.

  While the Census Bureau and the United States government used the term SMSA (by 1969 there were 233 of them), social scientists were also using new terms to describe the elusive, vaguely defined areas reaching out from what used to be simple “towns” and “cities”. A host of terms came into use: “metropolitan regions”,“poly-nucleated population groups”,“conurbations”,“metropolitan clusters”,“megalopolises” and so on.

  Question 30. According to the passage, the population of the United States was first classified as rural or urbanin _______.

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  The changing profile of a city in the United States is apparent in the shifting definitions used by the United States Bureau of the Census. In 1870 the census officially distinguished the nation’s “urban” from its “rural” population for the first time. “Urban population” was defined as persons living in towns of 8,000 inhabitants or more. But after 1900 it meant persons living in incorporated places having 2,500 or more inhabitants.

  Then, in 1950 the Census Bureau radically changed its definition of urban to take account of the new vagueness of city boundaries. In addition to persons living in incorporated units of 2,500 or more, the census now included those who lived in unincorporated units of that size, and also all persons living in the densely settled urban fringe, including both incorporated and unincorporated areas located around cities of 50,000 inhabitants or more. Each such unit, conceived as an integrated economic and social unit with a large population nucleus, was named a Standard Metropolitan Statistical Area (SMSA).

  Each SMSA would contain at least (a) one central city with 50,000 inhabitants or more or (b) two cities having shared boundaries and constituting, for general economic and social purposes, a single community with a combined population of at least 50,000, the smaller of which must have a population of at least 15,000. Such an area would include the county in which the central city was located, and adjacent counties that were found to be metropolitan in character and economically and socially integrated with the county of the central city.By 1970, about two-thirds of the population of the United States was living in these urbanized areas, and of that figure more than half were living outside the central cities.

  While the Census Bureau and the United States government used the term SMSA (by 1969 there were 233 of them), social scientists were also using new terms to describe the elusive, vaguely defined areas reaching out from what used to be simple “towns” and “cities”. A host of terms came into use: “metropolitan regions”,“poly-nucleated population groups”,“conurbations”,“metropolitan clusters”,“megalopolises” and so on.

  Question 33: According to the passage, why did the Census Bureau revise the definition of urban in 1950?

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  The changing profile of a city in the United States is apparent in the shifting definitions used by the United States Bureau of the Census. In 1870 the census officially distinguished the nation’s “urban” from its “rural” population for the first time. “Urban population” was defined as persons living in towns of 8,000 inhabitants or more. But after 1900 it meant persons living in incorporated places having 2,500 or more inhabitants.

  Then, in 1950 the Census Bureau radically changed its definition of urban to take account of the new vagueness of city boundaries. In addition to persons living in incorporated units of 2,500 or more, the census now included those who lived in unincorporated units of that size, and also all persons living in the densely settled urban fringe, including both incorporated and unincorporated areas located around cities of 50,000 inhabitants or more. Each such unit, conceived as an integrated economic and social unit with a large population nucleus, was named a Standard Metropolitan Statistical Area (SMSA).

  Each SMSA would contain at least (a) one central city with 50,000 inhabitants or more or (b) two cities having shared boundaries and constituting, for general economic and social purposes, a single community with a combined population of at least 50,000, the smaller of which must have a population of at least 15,000. Such an area would include the county in which the central city was located, and adjacent counties that were found to be metropolitan in character and economically and socially integrated with the county of the central city.By 1970, about two-thirds of the population of the United States was living in these urbanized areas, and of that figure more than half were living outside the central cities.

  While the Census Bureau and the United States government used the term SMSA (by 1969 there were 233 of them), social scientists were also using new terms to describe the elusive, vaguely defined areas reaching out from what used to be simple “towns” and “cities”. A host of terms came into use: “metropolitan regions”,“poly-nucleated population groups”,“conurbations”,“metropolitan clusters”,“megalopolises” and so on.

  Question 32: Prior to 1900, how many inhabitants would a town have to have before being defined as urban?

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  The changing profile of a city in the United States is apparent in the shifting definitions used by the United States Bureau of the Census. In 1870 the census officially distinguished the nation’s “urban” from its “rural” population for the first time. “Urban population” was defined as persons living in towns of 8,000 inhabitants or more. But after 1900 it meant persons living in incorporated places having 2,500 or more inhabitants.

  Then, in 1950 the Census Bureau radically changed its definition of urban to take account of the new vagueness of city boundaries. In addition to persons living in incorporated units of 2,500 or more, the census now included those who lived in unincorporated units of that size, and also all persons living in the densely settled urban fringe, including both incorporated and unincorporated areas located around cities of 50,000 inhabitants or more. Each such unit, conceived as an integrated economic and social unit with a large population nucleus, was named a Standard Metropolitan Statistical Area (SMSA).

  Each SMSA would contain at least (a) one central city with 50,000 inhabitants or more or (b) two cities having shared boundaries and constituting, for general economic and social purposes, a single community with a combined population of at least 50,000, the smaller of which must have a population of at least 15,000. Such an area would include the county in which the central city was located, and adjacent counties that were found to be metropolitan in character and economically and socially integrated with the county of the central city.By 1970, about two-thirds of the population of the United States was living in these urbanized areas, and of that figure more than half were living outside the central cities.

  While the Census Bureau and the United States government used the term SMSA (by 1969 there were 233 of them), social scientists were also using new terms to describe the elusive, vaguely defined areas reaching out from what used to be simple “towns” and “cities”. A host of terms came into use: “metropolitan regions”,“poly-nucleated population groups”,“conurbations”,“metropolitan clusters”,“megalopolises” and so on.

  Question 29: What does the passage mainly discuss?

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  The changing profile of a city in the United States is apparent in the shifting definitions used by the United States Bureau of the Census. In 1870 the census officially distinguished the nation’s “urban” from its “rural” population for the first time. “Urban population” was defined as persons living in towns of 8,000 inhabitants or more. But after 1900 it meant persons living in incorporated places having 2,500 or more inhabitants.

  Then, in 1950 the Census Bureau radically changed its definition of urban to take account of the new vagueness of city boundaries. In addition to persons living in incorporated units of 2,500 or more, the census now included those who lived in unincorporated units of that size, and also all persons living in the densely settled urban fringe, including both incorporated and unincorporated areas located around cities of 50,000 inhabitants or more. Each such unit, conceived as an integrated economic and social unit with a large population nucleus, was named a Standard Metropolitan Statistical Area (SMSA).

  Each SMSA would contain at least (a) one central city with 50,000 inhabitants or more or (b) two cities having shared boundaries and constituting, for general economic and social purposes, a single community with a combined population of at least 50,000, the smaller of which must have a population of at least 15,000. Such an area would include the county in which the central city was located, and adjacent counties that were found to be metropolitan in character and economically and socially integrated with the county of the central city.By 1970, about two-thirds of the population of the United States was living in these urbanized areas, and of that figure more than half were living outside the central cities.

  While the Census Bureau and the United States government used the term SMSA (by 1969 there were 233 of them), social scientists were also using new terms to describe the elusive, vaguely defined areas reaching out from what used to be simple “towns” and “cities”. A host of terms came into use: “metropolitan regions”,“poly-nucleated population groups”,“conurbations”,“metropolitan clusters”,“megalopolises” and so on.

  Question 35: The word “constituting” in paragraph 3 is closest in meaning to _______.

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  The changing profile of a city in the United States is apparent in the shifting definitions used by the United States Bureau of the Census. In 1870 the census officially distinguished the nation’s “urban” from its “rural” population for the first time. “Urban population” was defined as persons living in towns of 8,000 inhabitants or more. But after 1900 it meant persons living in incorporated places having 2,500 or more inhabitants.

  Then, in 1950 the Census Bureau radically changed its definition of urban to take account of the new vagueness of city boundaries. In addition to persons living in incorporated units of 2,500 or more, the census now included those who lived in unincorporated units of that size, and also all persons living in the densely settled urban fringe, including both incorporated and unincorporated areas located around cities of 50,000 inhabitants or more. Each such unit, conceived as an integrated economic and social unit with a large population nucleus, was named a Standard Metropolitan Statistical Area (SMSA).

  Each SMSA would contain at least (a) one central city with 50,000 inhabitants or more or (b) two cities having shared boundaries and constituting, for general economic and social purposes, a single community with a combined population of at least 50,000, the smaller of which must have a population of at least 15,000. Such an area would include the county in which the central city was located, and adjacent counties that were found to be metropolitan in character and economically and socially integrated with the county of the central city.By 1970, about two-thirds of the population of the United States was living in these urbanized areas, and of that figure more than half were living outside the central cities.

  While the Census Bureau and the United States government used the term SMSA (by 1969 there were 233 of them), social scientists were also using new terms to describe the elusive, vaguely defined areas reaching out from what used to be simple “towns” and “cities”. A host of terms came into use: “metropolitan regions”,“poly-nucleated population groups”,“conurbations”,“metropolitan clusters”,“megalopolises” and so on.

  Question 34: The word “those” in paragraph 2 refers to _______.

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  Under certain circumstances, the human body must cope with gases at greater-than-normal atmospheric pressure. For example, gas pressures increase rapidly during a drive made with scuba gear because the breathing equipment allows divers to stay underwater longer and dive deeper. The pressure exerted on the human body increases by 1 atmosphere for every 10 meters of depth on seater, so thay at 39 meters in seawater a diver is exposed to pressure of about 4 atmosphere. The pressure of the gases being breathed must equal the external pressure applied to the body, otherwise breathing is very difficult. Therefore all of the gases in the air breathed by a scuba diver at 40 meter are present at five times their usual pressure. Nitrogen, which composes 80 percent of the air we breathe, usually causes a balmy feeling of well-being at this pressure. At a depth of 5 atmosphere, nitrogen causes symptoms resembling alcohol intoxication, known as nitrogen narcosis. Nitrogen narcosis apparently results from a direct effect on the brain of the large amounts of nitrogen dissolved in the blood. Deep dives are less dangerous if helium is substituted for nitrogen, because under these pressures helium does not exert a similar narcotic effect. Asa scuba diver descends, the pressure of nitrogen on the lungs increases. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues. The reverse occurs when the diver surfaces, the nitrogen pressure in the lungs falls and the nitrogen diffuses from the tissues into the blood, and from the blood into the lungs. If the return to the surface is too rapid, nitrogen in the tissues and blood cannot diffuse out rapidly enough and nitrogen bubbles are formed. They can cause severe pains, particularly around the joints. Another complication may result if the breath is held during ascent. During ascent from a depth of 10 meters, the volume of air in the lungs will double because the air pressure at the surface is only half of what it was at 10 meters. This change in volume may cause the lungs to distend ang even rupture. This the rise of the exhaled air bubbles, and must exhale during ascent.

  Question:What should a diver do when ascending?

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  Under certain circumstances, the human body must cope with gases at greater-than-normal atmospheric pressure. For example, gas pressures increase rapidly during a drive made with scuba gear because the breathing equipment allows divers to stay underwater longer and dive deeper. The pressure exerted on the human body increases by 1 atmosphere for every 10 meters of depth on seater, so thay at 39 meters in seawater a diver is exposed to pressure of about 4 atmosphere. The pressure of the gases being breathed must equal the external pressure applied to the body, otherwise breathing is very difficult. Therefore all of the gases in the air breathed by a scuba diver at 40 meter are present at five times their usual pressure. Nitrogen, which composes 80 percent of the air we breathe, usually causes a balmy feeling of well-being at this pressure. At a depth of 5 atmosphere, nitrogen causes symptoms resembling alcohol intoxication, known as nitrogen narcosis. Nitrogen narcosis apparently results from a direct effect on the brain of the large amounts of nitrogen dissolved in the blood. Deep dives are less dangerous if helium is substituted for nitrogen, because under these pressures helium does not exert a similar narcotic effect. Asa scuba diver descends, the pressure of nitrogen on the lungs increases. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues. The reverse occurs when the diver surfaces, the nitrogen pressure in the lungs falls and the nitrogen diffuses from the tissues into the blood, and from the blood into the lungs. If the return to the surface is too rapid, nitrogen in the tissues and blood cannot diffuse out rapidly enough and nitrogen bubbles are formed. They can cause severe pains, particularly around the joints. Another complication may result if the breath is held during ascent. During ascent from a depth of 10 meters, the volume of air in the lungs will double because the air pressure at the surface is only half of what it was at 10 meters. This change in volume may cause the lungs to distend ang even rupture. This the rise of the exhaled air bubbles, and must exhale during ascent.

  Question:The word “rupture” in bold in paragraph 3 is closest in meaning to ________.

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  A survey is a study, generally in the form of an interview or a ques­tionnaire, which provides information concerning how people think and act. In the United States, the best-known surveys are the Gallup poll and the Harris poll. As anyone who watches the news during presiden­tial campaigns knows, these polls have become an important part of political life in the United States.

  North Americans are familiar with the many "person on the street" interviews on local television news shows. While such interviews can be highly entertaining, they are not necessarily an accurate indication of public opinion. First,theyreflect the opinions of only those people who appear at a certain location. Thus, such samples can be biased in favor of commuters, middle-class shoppers, or factory workers, depending on which area the new people select. Second, television interviews tend to attract outgoing people who are willing to appear on the air, while they frighten away others who may feel intimidated by a camera. A survey must be based on aprecise,representative sampling if it is to genu­inely reflect a broad range of the population.

  In preparing to conduct a survey, sociologists must exercisegreat care in the wording of questions. An effective survey question must be simple and clear enough for people to understand it. It must also be specific enough so that there are no problems in interpreting the re­sults. Even questions that are less structured must be carefully phrased in order to elicitthe type of information desired. Surveys can beindispensablesources of information, but only if the sampling is done properly and the questions are worded accurately.

  There are two main forms of surveys: the interview and the ques­tionnaire. Each of these forms of survey research has its advantages. An interviewer can obtain a high response rate because people find it more difficult to turn down a personal request for an interview than to throw away a written questionnaire. In addition, an interviewer can go beyond written questions and probefor a subject's underlying feelings and reasons. However, questionnaires have the advantage of being cheaper and more consistent.

  Question 44:What does the passage mainly discuss?

• Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

  A survey is a study, generally in the form of an interview or a ques­tionnaire, which provides information concerning how people think and act. In the United States, the best-known surveys are the Gallup poll and the Harris poll. As anyone who watches the news during presiden­tial campaigns knows, these polls have become an important part of political life in the United States.

  North Americans are familiar with the many "person on the street" interviews on local television news shows. While such interviews can be highly entertaining, they are not necessarily an accurate indication of public opinion. First,theyreflect the opinions of only those people who appear at a certain location. Thus, such samples can be biased in favor of commuters, middle-class shoppers, or factory workers, depending on which area the new people select. Second, television interviews tend to attract outgoing people who are willing to appear on the air, while they frighten away others who may feel intimidated by a camera. A survey must be based on aprecise,representative sampling if it is to genu­inely reflect a broad range of the population.

  In preparing to conduct a survey, sociologists must exercisegreat care in the wording of questions. An effective survey question must be simple and clear enough for people to understand it. It must also be specific enough so that there are no problems in interpreting the re­sults. Even questions that are less structured must be carefully phrased in order to elicitthe type of information desired. Surveys can beindispensablesources of information, but only if the sampling is done properly and the questions are worded accurately.

  There are two main forms of surveys: the interview and the ques­tionnaire. Each of these forms of survey research has its advantages. An interviewer can obtain a high response rate because people find it more difficult to turn down a personal request for an interview than to throw away a written questionnaire. In addition, an interviewer can go beyond written questions and probefor a subject's underlying feelings and reasons. However, questionnaires have the advantage of being cheaper and more consistent.

  Question 45:According to the passage, one advantage of live interviews over questionnaires is that live interviews