Correct Answer - Option 4 : 42
Concept used:
Number = 10(Tens digit) + Unit digit
Ex:- 50 = 10 × 5 + 0 = 50
Calculation:
Let the unit and ten's digit of the number be x and 2x respectively
Number = 10(2x) + x = 21x
Interchanged number = 10x + 2x = 12x
Now, A/Q
21x - 12x = 18
⇒ 9x = 18
⇒ x = 2
Number = 21x = 21 × 2 = 42
∴ The required number is 42