Which data set has the greater standard deviation, data set K or data

Hi viktorija,

Since the GMAT is NEVER going to ask you to calculate the Standard Deviation, you have to think about what this question is REALLY testing you on. It's really about your basic understanding of the concept of Standard Deviation and how "spread out" a group of numbers is.

Given the minor 'restrictions' in the prompt and two Facts, the REAL issue is whether the elements in each set are duplicates or not.

The prompt tells us that there are two sets of numbers: Set K and Set L. But we're not told ANYTHING about those Sets. We're asked which has the larger Standard Deviation.

I think that most Test Takers can see that each of the two Facts (individually) just tells us a little bit about each Set of values. So both Facts are INSUFFICIENT.

Combined, we know...
Every element in Set K is a multiple of 3
Every element in Set L is a multiple of 9

Here are two simple examples:
Set K: {3, 3]
Set L: {9, 18]
Set L has the larger Standard Deviation.

Set K: {3, 6]
Set L: {9 9}
Set K has the larger Standard Deviation.
Combined, INSUFFICIENT

In the first example, I could have put 100s of numbers into Set K - if they were all 3s, then the Standard Deviation would still be the same (it would be 0, since all the elements are the same).
In the second example, I could have 100s of numbers into Set L - if they were all 9s, then the Standard Deviation would still be the same (it would be 0).
Thus, in THIS question, the number of terms really isn't the issue.

Final Answer:

GMAT assassins aren't born, they're made,
Rich