Standard Deviation Problem

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yvonne0923: Senior | Next Rank: 100 Posts; Posts: 96; Joined: Mon Mar 07, 2011 8:43 pmFollowed by: 1 member; Thanked: 1 times

by yvonne0923 » Fri May 06, 2011 12:00 pm

Is the standard deviation of Set A greater than the standard deviation of Set B?
(1) the range of A is greater than the range of B
(2) The sets have the same number of terms

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[spoiler]O.A: E[/spoiler]
My answer is B, since(1) definitely does not work, but (2)the sets have the same numbers of terms. Does it mean both sets have 7 terms(for example) or exactly same numbers?

Thanks,

[/spoiler]

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Source: Beat The GMAT — Data Sufficiency | Fri May 06, 2011 12:00 pm

force5: Legendary Member; Posts: 582; Joined: Tue Mar 08, 2011 12:48 amFollowed by: 6 members; Thanked: 61 times; GMAT Score:740

by force5 » Fri May 06, 2011 12:20 pm

i didnt like this question. what is the source?

well if i consider what you have written then i would answer E.

statement 1 talks about range which is insufficient to tell us about standard deviation.

statement 2 talks about same number of terms. it can have 2 terms each or 5 terms each. but we dont know the distribution. hence insufficient.

combining still insufficient

This doesnt make a good question. there has to be something missing in this question.

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Arcane66: Senior | Next Rank: 100 Posts; Posts: 81; Joined: Sat Aug 08, 2009 1:16 pm; Thanked: 2 times

by Arcane66 » Fri May 06, 2011 6:45 pm

I got E too. I actually looked up standard deviation again and the basic formula for it. I know you can't tell from #1 or #2 alone. #1 doesn't tell you anything because all the terms in between the highest and lowest numbers could be disproportionately large or small. #2 by itself doesn't mean anything because we don't know the values. With both you still don't know because of the fact that you could have values skewed high or low.

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