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first set: (-101,-100,-99): mean (m) is -100, standard deviation is about 1 second set: (99,100,101): mean (m) is 100, standard deviation is about 1

1. or 2. for first set x will be -100 or between -100 and -99 that are lesser than 1 for second set x will be 100 or between 100 and 101 that are greater than 1

There is a set of number, the mean is m, the standard deviation is R, if add a number x to this set, is r<=R? ( r=std dev of new set) 1) x=m 2) m<x<m+R

There is a set of number, the mean is m, the standard deviation is R, if add a number x to this set, is r<=R? ( r=std dev of new set) 1) x=m 2) m<x<m+R

Dont know the answer, please explain.

Sorry Friends its r<=R not x<=R.

Maybe you could edit the original post also. I did the whole thing before I read your correction.

Stt1: x=m, since x is exactly the mean it will leave the std. deviation unchanged. r=R. So the info is SUFF to answer. Stt2: m<x<m+R => that x is larger than the mean. That means it is away from the center of the curve. So std. deviation must increase. (look at it like ( mean(x) - x(i) ) ^2 will add to the calcualtion of r). so r>R. So the info is SUFF to answer. Thus, IMO: D