Multiple choice general knowledge math & puzzles

While finding the average of ‘9’ consecutive numbers starting from X; a student interchanged the digits of second number by mistake and got the average which is 8 more than the actual. What is X?

  1. 14

  2. 18

  3. 20

  4. 30

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The second of the 9 consecutive numbers is X+1. Interchanging its digits raised the average by 8, so the sum increased by 9 x 8 = 72. Thus the interchanged number minus the original equals 72. For X=18, the second number is 19; 91 - 19 = 72, which fits. Other choices do not produce this difference.