Let, the unit’s digit = x
The ten’s digit = 12 – x
∴ The number = 10(12 – x) + x = 120 – 9x
After reversing,
Unit’s digit = 12 – x
Ten’s digit = x
∴The number after reversing = 10x + 12 – x = 9x + 12
According to problem,
⇒ 9x + 12 = 120 – 9x + 18
⇒ 18x = 126
⇒ x = 7
∴ The original number,
⇒ 120 – 9 × 7
⇒ 57