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Question

The sum of two digits of a 2-digit number is 9. If the number obtained by interchanging the digits exceeds the original number by 27, find the number.

This question was previously asked in
RRB NTPC 2025 Under Graduate CBT 1 Question Paper PDF (20-Jun-2026) (Shift 3)
The correct answer is

36

Let the number be \(10a+b\) with \(a+b=9\).

Interchanged number minus original: \((10b+a)-(10a+b) = 9(b-a) = 27 \Rightarrow b-a=3\).

Solving \(a+b=9\) and \(b-a=3\): \(b=6,\ a=3\).

Hence, the number is 36.

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