Sets A and B each contain six positive integers. Does the standard deviation of B exceed that of A?
(1) Every entry of B can be attained by multiplying a corresponding entry in A by a constant integer multiple k.
(2) Every entry in B is greater than every entry in A.
Answer:
(A) Statement 1 alone is sufficient, but statement 2 alone is not.
(B) Statement 2 alone is sufficient, but statement 1 alone is not.
(C) Both statements together are sufficient, but neither alone is sufficient.
(D) Each statement alone is sufficient.
(E) Neither statement is sufficient, even when combined.
The answer is E. Considering (1) by itself, A could equal B (k=1) or A could have a greater standard deviation than B (e.g., by setting k>1). Considering (2) by itself, A could be {1,2,3,4,5,6} and B could be {7,8,9,10,11,12}, which have the same standard deviation. Alternatively, A could be {1,1,1,2,2,2} and B could be {7,13,18,52,57,64}, in which case the standard deviation of B would exceed that of A. Finally, considering both statements together, it is apparent from the examples above that it is possible for the standard deviation of B to exceed that of A if both statements hold, but if A = {1,1,1,1,1,1} and B = {7,7,7,7,7,7} both statements are satisfied, AND both sets have the same standard deviation, zero. Hence the only possible answer is E.