The average of the first three numbers out of four numbers is 18 and that of the last three numbers is 20. If the last number is 25, what is the first number?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 19.
Let the four numbers be A, B, C, D
Sum of first 3 numbers = 18 × 3 = 54
Sum of last 3 numbers = 20 × 3 = 60
B + C + D = 60
A + B + C = 54
D = 25
(B + C + D) − (A + B + C) = 60 − 54
D − A = 6
25 − A = 6
A = 19