SD good Q

[anksgupta]

A set of data consists of the following 5 numbers : {0,2,4,6,8}

What 2 no.s if added to create a set of 7, will result in SD that is closest to the SD for set of 5 original nos.

1. -1,9
2. 4,4
3. 3,5
4. 2,6
5. 0,8

[DanaJ]

A quick look at the set you provided allows us to determine that the average of the set is 4.
The SD is actually a measurement of the average distance between the numbers of a set and the average of said set.
In this case, the SD is around 2. something. This is because the distance between 4 and (2 and 6) is 2, while the distance between 4 and (0 and 8) is 4. The average distance should be something like 3, but since we also have a 4 in the set (which is also the average - so the distance between 4 and 4 is zero), the SD is tilted towards 2 a little.

So you're basically looking for the set of numbers that are kind of 2 points away from the average and your best bet would be, IMHO, 2 and 6.

I may be wrong though, since statistics is not my favorite field.

[ssmiles08]

wow these kind of questions have me terrified Do these types have a realistic chance of appearing on the GMAT...the only reason I ask so is because it seems like you sort of have to find the actual standard deviation...unless there is some mystery method involved i haven't figured out yet??

[Claret]

Yes!! These questions have a fairly decent chance of appearing on the GMAT.

Infact i came across 2 SD questions on the gmat both on similar lines as the above question!!

I even remember the questions but revealing them would be against the gmac non-disclosure agreement !!

[ssmiles08]

Yes!! These questions have a fairly decent chance of appearing on the GMAT.

Infact i came across 2 SD questions on the gmat both on similar lines as the above question!!

I even remember the questions but revealing them would be against the gmac non-disclosure agreement !!

oh boy...fantastic (obvious sarcasm)........better get cracking then! Thanks Claret! Congrats on your GMAT score btw! it is still pretty darn good

[Claret]

thanks ssmiles08 ! i m going to re-take the test though !!

btw when is ur test ?

[ssmiles08]

thanks ssmiles08 ! i m going to re-take the test though !!

btw when is ur test ?

I am hoping for sometime in July...haven't registered yet...I have just started my verbal prep...so that will have to run its course and we'll see

apologies to anksgupta, for hijacking the thread for a little bit...hopefully you don't mind!

[niraj_a]

im thinking its 4 and 4 because since the difference between the remaining numbers i.e. 2 wont change this way, the SD wont change either.

did i get it right?

[Claret]

I am hoping for sometime in July...haven't registered yet...I have just started my verbal prep...so that will have to run its course and we'll see

Seeing your detailed explanations of math questions makes me think u ll definitely crack the test!!

All the very best

[anksgupta]

OA is D