**Explanation:**

Clearly, From 1 to 100, there are ten numbers with 5 as the unit's digit - 5, 15, 25, 35, 45, 55, 65, 75, 85, 95 and ten numbers with 5 as the ten's digit - 50, 51, 52, 53, 54, 55, 56, 57, 58, 59.

**So, required number = 10 + 10 = 20.**

In 55 there are two 5's ....one in one's digit and other in ten's digit

so we have counted 55 two times