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I'm not going to go into "how to solve" since many others are do it much better than I do.

I think for this question the key factors to know are: 1) definition of standard definition 2) definition of "0"

remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0. 0 is not a positive integer. (positive integer is > 0).

SD problems are the ones i miss and i failed here too....
_________________

Regards, Harsha

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat

On a side note, when a question tells you a set S has numbers x,y,z - do we assume that x y z will always be different numbers? or can they be the same number, but repeated 3 times.

BELOW IS REVISED VERSION OF THIS QUESTION:

Each term of set T is a multiple of 5. Is standard deviation of T positive?

The standard deviation of a set 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. So, basically we can say that it in a sense measures the distance and the distance can not be negative, which means that the standard deviation of any set is greater than or equal to zero: .

Next, the standard deviation of a set is zero if and only the set consists of identical numbers (or which is the same if the set consists of only one number).

(1) Each term of set T is positive --> if T={5} then then SD=0 but if set T={5, 10} then SD>0. Not sufficient.

(2) Set T consists of one term --> any set with only one term has the standard deviation equal to zero. Sufficient.

I'm not going to go into "how to solve" since many others are do it much better than I do.

I think for this question the key factors to know are: 1) definition of standard definition 2) definition of "0"

remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0. 0 is not a positive integer. (positive integer is > 0).

Sorry but is there some mistake here. Thought this helpful set of Bunuel

I'm not going to go into "how to solve" since many others are do it much better than I do.

I think for this question the key factors to know are: 1) definition of standard definition 2) definition of "0"

remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0. 0 is not a positive integer. (positive integer is > 0).

Sorry but is there some mistake here. Thought this helpful set of Bunuel

I'm not going to go into "how to solve" since many others are do it much better than I do.

I think for this question the key factors to know are: 1) definition of standard definition 2) definition of "0"

remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0. 0 is not a positive integer. (positive integer is > 0).

Sorry but is there some mistake here. Thought this helpful set of Bunuel

Although it's true that this problem is tests on the concept or definition of the standard deviation, I think that I'd like to further break up my the evaluation of the two statements. Using the concept, here is how I'd solve this:

Set T = {5 * I} where I = 1, 3, 5, 7, ..., or n Question: Is SD = positive? S1: All member of T are positive. Here are some of rules: If the set consists of only one item, then SD = 0 (because mean is same as the item). If the set consists of evenly distributed number, then SD > 0 So, making use of these two rule, we know that this answer is not sufficient.

S2: T consists of only one number. In this case, we know that SD is always 0. So, the answer to the question is always no. Therefore, S2 is sufficient.