To choose the number we have to choose the units, tens and hundreds digits of the number in such a way that the number is divisible by 5. Recall that units digit of any number divisible by 5 is either 0 or 5. So, there are only 2 ways of choosing the units digit.

After choosing the units digit, we can choose any one of 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9 as the tens digit. So, for each way of selecting the unit digits, the tens digit can be chosen in 10 ways. What about the hundreds digit? This cannot be zero, if we want our number to be a 3 digit number. So, for each way of selecting the units and tens digits there are nine choices, 1, 2, 3, 4, 5, 6, 7, 8 and 9, for the hundreds digit. Using the general principle, we see that there are 2 × 9 × 10 ways of selecting a 3 digit number divisible by 5.