Three-digit numbers start in 100 and end in 999.
The total number in that range are 999 - 100 + 1 = 900.
Let's write the first numbers in the range:
100, 101, 102, 103, 104, 105, ..., 998, 999
It's clear that for every two numbers, there is one odd number and one even number. Half of the numbers are odd, thus the number of three-digit numbers that are odd is 900 / 2 = 450
There are 900 numbers between 100 and 999. Half of them are even and half
are odd. This means that there are 450 even and 450 odd numbers.
