Two hundred people were asked if they had read a book in the last month.The accompanying contingency table,cross-classified by age,is produced. Given that a respondent read a book in the last month,the probability that he or she is at least 30 years old is the closest to ________.
A) 0.33.
B) 0.46.
C) 0.65.
D) 0.88.

Question

Two hundred people were asked if they had read a book in the last month.The accompanying contingency table,cross-classified by age,is produced.  Given that a respondent read a book in the last month,the probability that he or she is at least 30 years old is the closest to ________.
A) 0.33. 
B) 0.46. 
C) 0.65. 
D) 0.88.

Quizplus · Accepted Answer

To calculate the desired probability, we need to use the information in the table about the subset of people who have read a book in the last month. According to the table, 60 people have read a book in the last month (cell C2). Of these 60 people, 36 are at least 30 years old (cells C3 and C4). Therefore, the probability that a respondent who read a book in the last month is at least 30 years old is:
P(at least 30 years old | read book) = 36/60 = 0.6
Therefore, the closest answer choice is B) 0.46.

Two Hundred People Were Asked If They Had Read a Book