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by resilient » Sun May 11, 2008 11:00 am
Set X consists of 8 integers. Is the standard deviation of set X equal to zero?

(1) The range of set X is equal to 3

(2) The mean of set X is equal to 5


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Re: sd

by Stuart@KaplanGMAT » Sun May 11, 2008 6:46 pm
resilient wrote:Set X consists of 8 integers. Is the standard deviation of set X equal to zero?

(1) The range of set X is equal to 3

(2) The mean of set X is equal to 5

The only way a set can have a SD of 0 is if all the terms are the same.

(1) range is 3. Well, if range > 0, then some of the terms are different. Therefore, the set definitely does NOT have a SD of 0: sufficient.

(2) mean is 5. Set could be {5,5,5} (so YES, SD=0) or set could be {3,5,7} (so NO, SD not = 0): insufficient.

(1) is suff and (2) isn't: choose (A).
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by resilient » Mon May 12, 2008 5:56 am
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