BTGmoderatorLU wrote: ↑

Wed Feb 26, 2020 6:33 am

Source: GMAT Prep

In the graduating class of a certain college, 48 percent of the students are male and 52 percent are female. In this class, 40 percent of the male and 20 percent of the female students are 25 years old or older. If one student in the class is randomly selected, approximately what is the probability that he or she will be less than 25 years old?

A. 0.9
B. 0.7
C. 0.45
D. 0.3
E. 0.25

The OA is B

We can let the total students = 1000.

Thus, there are 480 male students and 520 female students.

Since 60 percent of the male students are less than 25 years old, 0.6 x 480 = 288 are less than 25 years old.

Since 80 percent of the female students are less than 25 years old, 0.8 x 520 = 416 are less than 25 years old.

Thus, there are 288 + 416 = 704, rounded to 700, people who are less than 25 years old. Therefore, the probability that a randomly selected person is less than 25 years old is approximately 700/1000 = 0.7.

Answer: B