Q: In a set of numbers, the mean is m1 and std dev is sd1. You insert a number equal to m1 to the original set. What is the new std dev? (sd2>sd1 or sd2<sd1 or sd2=sd1 or can’t answer). I feel it’s option (D), since in a ‘set’, there cannot be any repeats, but actually it’s option (B).
So, why shouldn’t I select (D) ? @gregmat