Discussion

Explanation:

Since the average differs by 2.7, the difference in sum will be 2.7 × 10 = 27.

Let the original number is ab. 

Let the sum of the rest nine terms be x.

Sum of all 10 numbers including ‘ab’ = x + 10a + b

Sum of all 10 numbers including reverse number ‘ba’ = x + 10b + a

Difference in sum = (x + 10b + a) - (x + 10a + b) = 27

⇒ 9(b - a) = 27

⇒ (b - a) = 3

Alternately,
The difference in total due to reversing the number = (10b + a) - (10a + b) = 9(b - a)

Since average increases by 2.7, the total increases by 2.7 × 10 = 27.

⇒ 9(b - a) = 27

⇒ (b - a) = 3

Hence, option (d).

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