The average of 1st 3 of 4 numbers is 6 and of the last 3 are 3. If the sum of the first and the last number is 13. What is the last numbers?	Choose the correct choice from the following answers:
A) 4 B) 2 C) 6 D) 7 E) 8

Rationale: a + b + c = 18 b + c + d = 9 a + d = 13 a – d = 9 a + d = 13 2 d = 4 d = 2 answer : b
Answer: B