Data Sufficiency

If set T consists of odd integers divisible by 5, is the standard deviation of T positive?

1. All members of T are positive
2. T consists of only one member.

Q:1. 0 is neither positive nor negative. is that true.??

i doubt OA-..... B

Q2. if i calculate SD to be zero, then can i say SD for the set is positive.... i dont think so.

pl explain....thanks.

source: gmat club.

I think SD is always >=0 as it is sum of square of diff with mean divided by mean and taking squrt. Yes 0 is neither positive nor negative it is 0. So OA B is reasonable as you know for 1 elem SD=0.

For more than 1 elelm, if all same(2, 2, 2) SD = 0, for 1, 2, 3 SD >0

i agree what you say.

but my question is that: from B. we can conclude that SD=0 , which is neither positive nor negative.

so, are we answer the question: is SD +ve.

ok...i got it .. we cant say sd is positive....thats why OA is B.

thanks..buddy.

advita wrote:i agree what you say.

but my question is that: from B. we can conclude that SD=0 , which is neither positive nor negative.

so, are we answer the question: is SD +ve.

ok...i got it .. we cant say sd is positive....thats why OA is B.

thanks..buddy.

Hi,

for "yes/no" questions, a statement is sufficient when it gives a definite answer to the question; a definite "no" is just as good as a definite "yes".

Here, the question is "is the SD of the set positive?". From (2), we can conclude that the SD is definitely NOT positive, so (2) is sufficient.

It's when a statement gives you a "sometimes yes, sometimes no" answer that it's insufficient.