8
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Question 8 • Mathematics II

A survey of the 12 th grade students at Gaffigan High School found that 84 percent of the seniors have their driver’s licenses, 16 percent of seniors take the bus every day to school, and 14 percent of the seniors have driver’s licenses and take the bus to school every day. To the nearest whole percent, what is the probability that a senior takes the bus to school every day, given that he or she has a driver’s license?

Answer
A
36 percent
B
70 percent
C
17 percent
D
19 percent

Explanation

Use conditional probability: the probability a senior takes the bus given that the senior has a license is the percentage who both have licenses and take the bus divided by the percentage who have licenses. Calculate 14% ÷ 84% = 1/6, or about 16.7%. Rounded to the nearest whole percent, that is 17 percent, choice C.

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