The average (mean) of the five numbers $8,9,10,11,12$ is
(A) 12.5
(B) 8
(C) 9.6
(D) 9
(E) 10
The average of the five given numbers is $\frac{8+9+10+11+12}{5}=\frac{50}{5}=10$.

Alternatively, since there are an odd number of consecutive integers, the average is the middle number, which is 10 .

ANswer: (E)