The average age of 25 students of a class is 25 years. Out of these, the average age of 10 students is 22 years and that of the other 14 students is 28 years. The age of the 25th student is?
Choose the correct choice from the following answers
A) 10  B) 15  C) 13  D) 11  E) 9

Rationale: "age of the 25 th student = 25 * 25 - ( 10 * 22 + 14 * 28 ) = 625 - 612 = 13 years answer is c"
Answer: C