Multiple choice general knowledge math & puzzles

The average between a two digit number and the number obtained by interchanging the digits is 9. What is the difference between the two digits of the number?

  1. 8

  2. 2

  3. 5

  4. Cannot be determined
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let the number be 10a + b (where a and b are digits, a ≠ 0). The reversed number is 10b + a. Average = (10a + b + 10b + a) / 2 = 11(a + b) / 2 = 9. This gives a + b = 18/11. However, a and b must be integers (0-9), and 18/11 is not an integer. Therefore, no such two-digit number exists - the problem has no valid solution with whole number digits.

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