Multiple choice

While finding the average of 9 consecutive numbers starting from X, a student interchanged the digits of the second number by mistake and got the average 8 more than the actual average. Find the value of X.

  1. 13

  2. 15

  3. 17

  4. 18

  5. None of these
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D Correct answer
Explanation

Since the average is 8 more than the actual, the second number will increase by 72 (9 x 8) by interchanging the digits. If 'ab' is the second number, then 10a + b + 72 = 10b+ a, i.e. 9 (b - a) = 72b - a = 8 The possible number 'ab' is 19. Since the second number is 19, the first number is 18. So, X = 18

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