5. The ages of Grannie's seven grandchildren are consecutive positive integers. The youngest three grandchildren have a mean age of 6 . What is the mean age of the oldest three grandchildren?
A 8
B 9
C 10
D 11
E 12
5. C The ages of the youngest three grandchildren are three consecutive positive integers which have a mean of 6 . So they are $5,6,7$. Hence the ages of the other four grandchildren are $8,9,10,11$. Therefore the mean age of the oldest three grandchildren is $\frac{9+10+11}{3}=\frac{30}{3}=10$.