M11 q28

For the GMAT you only need to understand the concept of SD: you won't be asked to actually calculate the standard deviation of a set on the GMAT. So, what is the main thing you should know about it? Standard deviation shows how much variation there is from the mean, how widespread a given set is. So, a low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values.

Now, (1) says that the range of S is greater than the range of T, so the biggest and smallest numbers in S are more widespread than the biggest and smallest numbers in T. But what about the other numbers of these sets?

SD of {0, 10} is greater than SD of {0, 9}, but SD of {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10} is less than SD of {0, 9}. Not sufficient.

(2) The mean of set S is greater than the mean of set T. Info about the mean is totally useless to get how widespread the given sets are. Not sufficient.

(1)+(2) Statement (2) gives absolutely no new info for (1), so even taken together they are still insufficient to answer the question.

Answer: E.

Check this for more: math-standard-deviation-87905.html

PS questions on SD: ps-questions-about-standard-deviation-85897.html
DS questions on SD: ds-questions-about-standard-deviation-85896.html

Hope it helps.