Here is a group of 9 people.
Can we divide the group into pairs so that everyone has a partner?
A number is odd if we cannot split it into groups of two with nothing left over.
If we try to split these 9 squares into groups of 2, there is always one left over. So, 9 is odd.
Which of the following numbers is odd?
Here are 57 dots. Is 57 even or odd?