Data Sufficiency

Ques) 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

Please assist with above problem.

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

If every value in Set X is multiplied by a factor of N=2, then the value of mean M will also be multiplied by a factor of N=2.
If every value in Set X is multiplied by a factor of N=3, then the value of mean M will also be multiplied by a factor of N=3.
If every value in Set X is multiplied by a factor of N=10, then the value of mean M will also be multiplied by a factor of N=10.
Implication:
If we know the value of N, we can determine by what percent mean M will increase.

Question stem, rephrased:
What is the value of N?

Statement 1: Z=60
Since every value in Set X is known, the value of M can be determined.
No information about N.
INSUFFICIENT.

Statement 2: N = Z/M
Since the values of Z and M are unknown, no way to determine the value of N.
INSUFFICIENT.

Statements combined:
Statement 1: Z=60 enables us to determine the value of M.
Statement 2: Z=60 and the value of M will enable us to determine the value of N.
SUFFICIENT.

The correct answer is C.