The average age of a group of n people is 15 years old. One more person aged 35 joins the group and the new average is 17 years old. What is the value of n?  Choose the correct choice from the following options:
A) 8
B) 9
C) 10
D) 11
E) 12

Rationale: 15 n + 35 = 17 ( n + 1 ) 2 n = 18 n = 9 the answer is b .
Answer: B