How many even numbers between 1 and 21? You could just make a list of all the even numbers between 1 and 21 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 21.
We start by determining the first even number and last even number between 1 and 21. The numbers between 1 and 21 start with 2 and end with 20. That means that the first even number is 2 and the last even number is 20.
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 21?"
N = (Last - First + 2) ÷ 2
N = (20 - 2 + 2) ÷ 2
N = 20 ÷ 2
N = 10
Even numbers between 1 and 21 = 10
Even Numbers Between Calculator
Use the tool below to calculate the number of even numbers between another set of numbers.