Out of four numbers ,the average of first three is 16 and that of the last three is 15. If the last number is 20,the first number is :	Options:
A) 22  B) 23  C) 77  D) 99  E) 27
Explanation:   Let the numbers be a,b,c,d   Given, a + b + c = 48, b + c + d = 45   Now, d = 20   thus, b + c + 20 = 45 ⇒ b + c = 25   Putting the value of b + c in a + b + c = 48   a + 25 = 48 ⇒ a = 23   Answer: 23
<result>B</result>
Out of four numbers ,the average of first three is 16 and that of the last three is 15. If the last number is 20,the first number is :