A college chemistry course is divided into two sections.

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VJesus12: Legendary Member; Posts: 2276; Joined: Sat Oct 14, 2017 6:10 am; Followed by:3 members

A college chemistry course is divided into two sections.

by VJesus12 » Thu Apr 12, 2018 9:34 am

A college chemistry course is divided into two sections. In section A, the average score in the final examination was 92. In section B, the average score in the final examination was 84. If the average score of all 40 students in the course was 89, how many students are in section A?

(A) 15
(B) 18
(C) 20
(D) 22
(E) 25

The OA is the option E.

What is the equation that solves this PS question? Help, someone. Thanks in advanced.

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Source: Beat The GMAT — Problem Solving | Thu Apr 12, 2018 9:34 am

swerve: Legendary Member; Posts: 2499; Joined: Sun Oct 29, 2017 2:04 pm; Followed by:6 members

by swerve » Thu Apr 12, 2018 9:51 am

Hi VJesus12,

I solved this questions as follows,

A: Average: B
92: 89: 84

A: B
89-84: 92-89
5 : 3

If total Students are 40.
Then
A: B
25: 15
Option E.

Regards!

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8085; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Mon Apr 16, 2018 4:15 pm

VJesus12 wrote:A college chemistry course is divided into two sections. In section A, the average score in the final examination was 92. In section B, the average score in the final examination was 84. If the average score of all 40 students in the course was 89, how many students are in section A?

(A) 15
(B) 18
(C) 20
(D) 22
(E) 25

We can let the number of students in section A = A and the number of students in section B = B. Calculating the weighted average of the two sections, we have:

89 = (92A + 84B)/(A + B)

89A + 89B = 92A + 84B

5B = 3A

We also have:

A + B = 40

B = 40 - A

Thus:

5(40 - A) = 3A

200 - 5A = 3A

200 = 8A

A = 25

Answer: E

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