Data Sufficiency

If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the
mean M of the set increase?
(1) Z = 60 (2) N = Z / M

OA is [spoiler]C[/spoiler]

Mean of set = M

New mean will be = MN

% Increase = M(N-1)/M * 100 (or) (N-1)*100

we need to find N..

(1) doesnt give N
(2) doesnt give N

Together, we can find N.. C

In order to answer this question you need to recognize that you cannot find the mean of the original problem without X - the mean will be (26 + Z)/6 ane the percent change will be
[n(26+z)/6 - (26+Z)/6]/(26+z)/6 - thus you need both Z and N to solve the problem

1) give you Z but not n

2)N = Z/M gives you a relationship but does not help you to solve for Z or N

However when you put the two together you know that z = 60 and thus N=60/(26 +60)/6 - and you can solve for N and therefore it is sufficient.