Find a number less than 100 that is increased by one-fifth of its value when its digits are reversed.

Lets say the number is ab. Its value is 10a + b

When it is reversed it is 10b + a = 12a+1.2b (from the condition its value should increase 0.2 times).

11 a = 8.8b

a/b = 8.8/11 = 0.8/1 = 8/10 = 4/5 (we do this because a and b should be natural numbers less than 10).

answer is 45.