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What Are Odd Numbers? (Mathematics Lesson)

What Are Odd Numbers?

Odd numbers are integers that cannot be divided exactly by 2.

How to Check if a Number Is an Odd Number

Question: Is 25 an odd number?

Step 1
Divide the number by 2.
25 ÷ 2 = 12.5.

Step 2
If the number from Step 1 is a whole number, the original number is even. Else it is odd.
12.5 is not a whole number. 25 is an odd number.

Real Examples of Odd Numbers

Some examples of odd numbers are:

Quick Test
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Note

FORMAL DEFINITION OF ODD NUMBERS

A number n is odd if there exists an integer k, such that:



This means than n can never be divided exactly by 2 - if it is divided by 2 there will always be a remainder of 1.

A QUICK WAY TO CHECK IF A NUMBER IS AN ODD NUMBER

A number is odd if its last digit is 1, 3, 5, 7 or 9.