Math questions from and GMAT Prep software
Course Students
Posts: 33
Joined: Sat Apr 09, 2016 10:33 pm


by ASMAA997 Wed Jun 29, 2016 2:17 pm


Which of the following pairs of numbers, when added to the set above, will increase the standard deviation of the set?

I. 14, 16
II. 9, 21
III. 15, 100

(A) II only
(B) III only
(C) I and II
(D) II and III
(E) I, II, and III

this question I couldnt find the answer because when I add every # to the set the same SD is there . Ex:

let me take the third :
the mean is 15
SD: 3

the new set when I add 15 is
( 24, 27,30,33,36 )

( 109,112,115,118,121 )
the SD is still 3

So , may anyone explain it for me and where is my main mistake ?
Posts: 19747
Joined: Tue Aug 14, 2007 8:23 am

Re: SD

by RonPurewal Sun Jul 03, 2016 4:25 am

the problem is talking about appending numbers to the set. (this should have been clear from the fact that the choices are pairs of numbers—clearly you can't add a pair of numbers to something at the same time!) so, for instance, the first option would create the set 9, 12, 14, 15, 16, 18, 21.

beyond that, this problem is in the wrong folder. if you still have questions about it, you'll have to post it in the correct folder (with a citation of the source, if necessary). thank you.