Standard Dev shortcut

[Goldust]

Here's the simplest example that I could come up with to answer the original query. Consider two sets of numbers : {3,7} and {3,5,7}.

Now, both have the same range, but the S.D. of the second set is lower than that of the first set.

Continuing like this {3,5,5,...,5,5,7} would have lower and lower S.Ds without the range being any different.

[Jeanette]

Okay, I get it.

On GRE's you'll often see sets like this:

2,3,4,5,6

Or

2,3,3,5,6,6

Which one has the greater standard dev?

[chestnut.cc]

the same actually :s

[Oldman]

I've also seen them in PP where you have a variable listed with other numbers and you have to determine which number out of the answer choices will give you the smallest deviation.

I've also seen a DI section based on deviations. For the GRE, they don't expect deep knowledge of advanced topics. They just use deviations to test your ability to think abstractly about averages. With your scores, you'll do fine and probably won't even see one of these questions.