Question

A student ID number is a letter of the alphabet followed by 2 digits. How many different IDs are possible if the digits can be repeated?

Answer 1

First, there are 26 distinct alphabets and 10 distinct digit numbers.

Then, the first digit of ID has 26 possibilities.

For the rest of 2 digits, the total cases are 10*10 = 100 possibilities.

However, there are 10 cases are repeated when two digits are the same. so you have to subtract it by 10

So answer will be 26 * (100-10) = 23400