1) Not necessarily. The set

{6,8,10}

has a lower standard deviation than the set

{5,8,11}

However, the SD of the set

{6,7,8}

is equal to that of

{7,8,9}

Does that help?

Thanks.. Please can you explain my second question too?For example, what is the solution for a problem like this


A certain list of 100 data has an average of 6 and a SD deviation of d, where d is positive.Which of the following pairs of data, when added to the list, must result in set of 102 data with SD less than d?

[A]-6,0

0,0

[C]0,6

[D]0,12

[E]6,6


Please explain

I think to best understand SD is to know how to calculate SD.

The answer to your question is E, 6, 6, because it reduces SD by adding two more terms without increasing the variance.

To answer your previous question, I don't think you need to worry about not altering SD for GMAT. As for reducing SD, you can do so by adding numbers to the set that are closer to the average than the existing numbers, and for increasing SD, do the opposite, which is to add numbers that are larger than the average.