Difficult to solve

Solution:

Let the tens digit be x and the ones digit be y.

x + y = 15 … (1)

Original number = 10x + y

Reverse number = 10y + x

10y + x = 10x + y + 9 (Given)

⇒ 9y – 9x = 9

⇒ y – x = 1 … (2)

Adding (1) and (2),

=> x + y + y - x = 15 + 1
=> 2y = 16

⇒ y = 8

When y = 8,

x + 8 = 15 ( from (1) )

x = 15 – 8 = 7

∴ Original number = 10x + y = 10 × 7 + 8 = 70 + 8 = 78

Hence, the number is 78