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If the average (arithmetic mean) of

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boomgoesthegmat Senior | Next Rank: 100 Posts Default Avatar
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If the average (arithmetic mean) of

Post Thu Apr 28, 2016 1:41 pm
If the average (arithmetic mean) of the four numbers 3, 15, 32, and (N + 1) is 18, then N =

A) 19
B) 20
C) 21
D) 22
E) 29

C

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Post Thu Apr 28, 2016 2:08 pm
(3 + 15 + 32 + n + 1) / 4 = 18

51 + n = 4 * 18

n = 72 - 51

n = 21

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Post Thu Apr 28, 2016 1:45 pm
boomgoesthegmat wrote:
If the average (arithmetic mean) of the four numbers 3, 15, 32, and (N + 1) is 18, then N =

A) 19
B) 20
C) 21
D) 22
E) 29
If the average of the four numbers is 18, then we know that [3 + 15 + 32 + (N+1)]/4 = 18
Multiply both sides by 4 to get: 3 + 15 + 32 + (N+1) = 72
Simplify: 51 + N = 72
Solve: N = 21
Answer: C


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The following video covers the concepts/strategies that are useful for answering this question:
- Mean, median and mode: https://www.gmatprepnow.com/module/gmat-statistics/video/800

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