The mean (average) of 6,9 and 18 is equal to the mean (average) of 12 and $y$. What is the value of $y$ ?
(A) 22
(B) 21
(C) 10
(D) 11
(E) 5
The mean of 6,9 and 18 is $\frac{6+9+18}{3}=\frac{33}{3}=11$.

Since the mean of 12 and $y$ is thus 11 , then the sum of 12 and $y$ is $2(11)=22$, so $y=10$.

ANSWER: (C)