Probability that two digit number is multiple of five and how?

the smallest 2 digit number is 10, the largest is 99

How many is that ? ---> sum1

multiples of 5 are all those that end in zero or end in 5
e.g. 10, 20 , ... 90
15, 25, 35 ... 95
how many is that --> sum2
prob = sum2/sum1