Question

The tenth digit number is twice the unit digit the number obtained by interchanging the digit is 39 less than original no find the no

Answer 1

let unit digit be x
tens digit = 2x
number = 2x ×10 + x
= 21x
interchanging number = x × 10 + 2x
= 12x
a to q
21x - 39 = 12x
21x - 12x = 39
9x = 39
x = 39/9
x= 13/3
unit digit = 13/3
tens digit = 2 × 13/3
= 26/3
number = 21 × 13 /3
= 7 × 13
= 91