In a certain class, 70% of the students learn Physics...

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swerve: Legendary Member; Posts: 2535; Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

by swerve » Thu Apr 05, 2018 9:11 am

In a certain class, 70% of the students learn Physics and 65% of the students learn Chemistry. What is the smallest percentage of those who learn both Physics and Chemistry?

A. 25%
B. 30%
C. 35%
D. 40%
E. 45%

The OA is C.

I tried to solve this PS question but I can't get the correct answer. Please, can anyone help me with it? Thanks.

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Source: Beat The GMAT — Problem Solving | Thu Apr 05, 2018 9:11 am

Vincen: Legendary Member; Posts: 2898; Joined: Thu Sep 07, 2017 2:49 pmFollowed by: 5 members; Thanked: 6 times

by Vincen » Fri Apr 06, 2018 1:17 am

swerve wrote:In a certain class, 70% of the students learn Physics and 65% of the students learn Chemistry. What is the smallest percentage of those who learn both Physics and Chemistry?

A. 25%
B. 30%
C. 35%
D. 40%
E. 45%

The OA is C.

I tried to solve this PS question but I can't get the correct answer. Please, can anyone help me with it? Thanks.

Hello swerve.

This is the way I'd solve it.

Let's suppose that there are 100 students.

Then 70 students learn Physics, which implies that there are 30 students that learn just Chemistry.

Since there are 65 students that learn Chemistry, this implies that 35 students learn just Physics.

Therefore, there are 30+35=65 students that learn just a topic. Hence, there are 35 students who learn both Physics and Chemistry.

This is why the correct answer is C.

I really hope this can help you.

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Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

by Jeff@TargetTestPrep » Tue Apr 10, 2018 10:28 am

swerve wrote:In a certain class, 70% of the students learn Physics and 65% of the students learn Chemistry. What is the smallest percentage of those who learn both Physics and Chemistry?

A. 25%
B. 30%
C. 35%
D. 40%
E. 45%

[Note: Here we are assuming that every student learns either Physics or Chemistry or both.]

Let's let b = the number of students learning both Physics and Chemistry. Let's also assume that there are 100 students. Since 70% of the students learn Physics and 65% of the students learn Chemistry, we could say that:

100 = 65 + 70 - b

100 = 135 - b

b = 35

Answer: C

Jeffrey Miller
Head of GMAT Instruction
[email protected]

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