There are four numbers. If we leave out any one number, the average of the

Q: There are four numbers. If we leave out any one number, the average of the remaining three numbers will be 45, 60, 65 or 70. What is the average of all four numbers?
A. 50
B. 55
C. 60
D. 65

Answer: C

If the four numbers are A, B, C and D, then we know that

  • A + B + C = 45 × 3
  • A + B + D = 60 × 3
  • A + C + D = 65 × 3
  • B + C + D = 70 × 3

Now add them up to get 3+ 3B + 3C + 3D = (45 + 60 + 65 + 70) × 3

Which is A + B + C + D = (45 + 60 + 65 + 70) = 240So their average is 240/4 = 60