How many odd numbers between 2 and 21? You could just make a list of all the odd numbers between 2 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 odd numbers there are between 2 and 21.
We start by determining the first odd number and last odd number between 2 and 21. The numbers between 2 and 21 start with 3 and end with 20. That means that the first odd number is 3 and the last odd number is 19.
Now you add 2 to the difference of the last odd number and the first odd number, and then divide the sum by 2. Here is the formula and the answer to "How many odd numbers between 2 and 21?"
N = (Last - First + 2) ÷ 2
N = (19 - 3 + 2) ÷ 2
N = 18 ÷ 2
N = 9
Odd numbers between 2 and 21 = 9
Odd Numbers Between Calculator
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