Source: Official Guide for the GMAT 13th Ed. Data Sufficiency; #109 Official Guide for the GMAT 2015 14th Ed. Data Sufficiency; #109

3

List M (not shown) consists of 8

List M (not shown) consists of 8 different integers, each of which is in the list shown. What is the standard deviation of the numbers in list M?

2 Explanations

1

Siddharth Sahasrabudhe

Statement 1: The average of the numbers in list M is equal to average of the numbers in the list shown.Since it is evenly spaced list the mean of the two list should be 13.
Mean of list M is 13. Hence list M should also be evenly spaced. the only way we can get the mean =13 from list M, is by eliminating the outliers 4,22 from the original list. Hence the list M is (6,8,10,12,14,16,18,20)
The standard deviation will be same as the original list.

Hence should the choice A stands as correct choice? Please correct my interpretation.

Jul 8, 2015 • Comment

Jonathan , Magoosh Tutor

Hi Siddharth! Removing 4 and 22 is not the only way to keep the same mean of 13. We could remove any two numbers that are equidistant from the mean and on opposite sides of it. For example, we could remove 6 and 20, or 8 and 18. We will have the same mean. But the standard deviation will change. So (1) is not sufficient. I hope that helps.

Jul 10, 2015 • Reply

2

Gravatar Mike McGarry, Magoosh Tutor

Jan 4, 2014 • Comment

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Section 6.3 Data Sufficiency

Section 6.3 Data Sufficiency

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