How many even numbers between 1 and 20? How many even numbers between 1 and 20? You could just make a list of all the even numbers between 1 and 20 and then count them, but what fun would that be?

Instead, we have created this simple process with a small formula to calculate exactly how many even numbers there are between 1 and 20.

We start by determining the first even number and last even number between 1 and 20. The numbers between 1 and 20 start with 2 and end with 19. That means that the first even number is 2 and the last even number is 18.

Now you add 2 to the difference of the last even number and the first even number, and then divide the sum by 2. Here is the formula and the answer to "How many even numbers between 1 and 20?"

N = (Last - First + 2) ÷ 2
N = (18 - 2 + 2) ÷ 2
N = 18 ÷ 2
N = 9
Even numbers between 1 and 20 = 9

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