Question

The sum of two digits of a two digit number is 9 the number obtaining by reversed the order of digits is 9 less than twice the original number, find the number

Answer 1

Sum of the digits is 9.

∴The number could be 18, 27, 36, 45, 54, 63, 72, 81.

Reversing the order of the digits gives us a number 9 less than twice the original number.

∴By using trial and error, we can find the number,

18→ 18 x 2 -9 = 27 ≠ 81              X

27→ 27 x 2 -9 = 45 ≠ 72            X

36→ 36 x 2 -9 = 63 = 63            √

45→ 45 x 2 -9 = 81 ≠ 54            X

54→ 54 x 2 -9 = 99 ≠ 45           X

63→ 63 x 2 -9 = 117 ≠ 36           X

72→ 72 x 2 -9 = 135 ≠ 27           X

81→ 81 x 2 +9 = 153 ≠ 18           X

∴The number is 36.

:)