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What is the standard deviation of the set A? 1) Mean of the

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What is the standard deviation of the set A? 1) Mean of the

by GMATinsight » Mon May 22, 2017 7:19 am
What is the standard deviation of the set A?

1) Mean of the set A is 10
2) Range of the set A is 0

Source: www.GMATinsight.com

Answer: option B
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What is the standard deviation of the set A? 1) Mean of the

by Brent@GMATPrepNow » Mon May 22, 2017 7:27 am
GMATinsight wrote:What is the standard deviation of set A?

1) Mean of the set A is 10
2) Range of the set A is 0
Target question: What is the standard deviation of set A?

Statement 1: Mean of the set A is 10
There are several sets that satisfy statement 1. Here are two:
Case a: Set A = {10, 10, 10}. The mean = 10. In this case, the standard deviation of set A is 0
Case b: Set A = {0, 10, 20}. The mean = 10. In this case, the standard deviation of set A is NOT 0
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: Range of the set A is 0
If the range is 0, then every value in set A is the same.
In other words, the the standard deviation of set A is 0
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer: B

Cheers,
Brent
Last edited by Brent@GMATPrepNow on Tue Aug 28, 2018 2:09 pm, edited 1 time in total.
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by DavidG@VeritasPrep » Mon May 22, 2017 7:30 am
A good official question testing the same concept: https://www.beatthegmat.com/standard-dev ... 76816.html
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