In the graduating class of a certain college, 48 percent of

[BTGmoderatorDC]

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

OA B

Source: GMAT Prep

[GMATGuruNY]

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

Every student is EITHER male OR female.
Every student is EITER older OR younger.
For an EITHER/OR problem, use a DOUBLE MATRIX to organize the data:

_______________M______F_______Total

older:

younger:

total:



Let total students = 100:

_______________M______F_______Total

older:

younger:

total:__________________________100



48% males, 52% females.
Since we're looking for an approximation, let's say that 50% are males and 50% are females:

_________________M______F_______Total

older:

younger:

total:__________50_____50________100



40% of the males and 20% of the females are 25 and older:

_________________M______F_______Total

older:__________20_____10_______

younger:

total:__________50_____50________100


Complete the matrix:

_________________M______F_______Total

older:__________20_____10________30

younger:_______30_____40________70

total:__________50_____50________100


P(younger) = 70/100 = 0.7.

The correct answer is B.

[Brent@GMATPrepNow]

I thought I'd point out that Mitch's Double Matrix Method approach can be used for most questions featuring a population in which each member has two characteristics associated with it.
Here, we have a population of students, and the two characteristics are:
- male or female
- younger than 25 or older than 25

This question type is VERY COMMON on the GMAT, so be sure to master the technique.

To learn more about the Double Matrix Method, watch this video: https://www.gmatprepnow.com/module/gmat- ... ems?id=919

Once you're familiar with this technique, you can attempt these additional practice questions:

Easy Problem Solving questions
- https://www.beatthegmat.com/finance-majo ... 67425.html

Medium Problem Solving questions
- https://www.gmatprepnow.com/module/gmat- ... /video/920
- https://www.beatthegmat.com/posted-speed ... 72374.html
- https://www.beatthegmat.com/motel-t271938.html
- https://www.beatthegmat.com/of-the-appli ... 70255.html
- https://www.beatthegmat.com/opening-nigh ... 64869.html
- https://www.beatthegmat.com/at-least-100 ... 74669.html
- https://www.beatthegmat.com/prblem-solving-t279424.html

Difficult Problem Solving questions
- https://www.gmatprepnow.com/module/gmat- ... /video/946
- https://www.beatthegmat.com/ratio-problem-t268339.html
- https://www.beatthegmat.com/overlapping- ... 65223.html
- https://www.beatthegmat.com/fractions-t264254.html
- https://www.beatthegmat.com/overlapping- ... 64092.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-2

Easy Data Sufficiency questions
- https://www.gmatprepnow.com/module/gmat- ... /video/943
- https://www.beatthegmat.com/for-what-per ... 70596.html
- https://www.beatthegmat.com/ds-quest-t187706.html

Medium Data Sufficiency questions
- https://www.beatthegmat.com/sets-matrix-ds-t271914.html
- https://www.beatthegmat.com/each-of-peop ... 71375.html
- https://www.beatthegmat.com/a-manufacturer-t270331.html
- https://www.beatthegmat.com/in-costume-f ... 69355.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-1

Difficult Data Sufficiency questions
- https://youtu.be/dsCeqF9Kbk8
- https://www.beatthegmat.com/double-set-m ... 71423.html
- https://youtu.be/dOZ9KM1m5Hs
- https://www.beatthegmat.com/sets-t269449.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-3

Cheers,
Brent