Question

If the ten's digit no. of a two digit no. is twice the unit digit. When the digits are interchanged their sum will be 111​

Answer 1

Method 1: Let the number be 10x+y.

x=3y …(1)

10x+y-36 = 10y+x, or

9x=9y+36, or

x=y+4 …(2)

Equate (1) and (2),

3y = y+4, or

y = 2 and x = 6.

So the number is 62.

Method 2: Consider the numbers 31, 62, 93.

Subtract 36 from each of the above numbers : -5, 26, 44.

The number is 62 which gets reversed to 26 when you subtract 36 from it.

Answer : 62.

hope this help you