What is this skill?
An even number can be split into two equal groups, or into pairs, with nothing left over. An odd number always has one left over. Second graders learn that 8 is even because 8 counters make 4 pairs, and 9 is odd because 9 counters make 4 pairs and one extra. Even numbers can also be written as a doubles fact, like 4 + 4 = 8.
Once children have that meaning, they learn the shortcut: look only at the ones digit. Numbers ending in 0, 2, 4, 6 or 8 are even, and numbers ending in 1, 3, 5, 7 or 9 are odd. So 74 is even and 63 is odd, no matter how big the tens digit is.
Why it matters
Even and odd numbers are a child’s first look at number patterns and a gentle introduction to reasoning about why something is always true. Why is the ones digit enough? Because every ten can be split into five pairs, so only the ones decide whether there is a leftover. That kind of explanation is what mathematicians do.
The idea comes back often. It helps with doubles and halves, sharing things fairly, skip counting by 2s, arrays with two rows, and later with multiplication and division facts. Children who know that two odd numbers add up to an even number have a quick way to spot a mistake in their own work.
Common mistakes
- Looking at the tens digit instead of the ones, and deciding 47 is even because 4 is even. Cover the tens digit with a finger and ask about the digit that is left.
- Thinking zero is neither even nor odd. Zero is even: zero objects split into two equal groups of zero, with nothing left over, and it ends the 2, 4, 6, 8 pattern.
- Memorizing the list of digits without the meaning, so a child cannot explain why 14 is even. Building numbers with pairs of counters keeps the reason in view.
- Confusing "odd" in math with the everyday meaning of strange. A quick conversation that odd numbers are the ones with an "odd one out" can turn the mix-up into a memory aid.
How to help at home
- Pair up socks, shoes or spoons and ask whether everything has a partner. If one is left over, the number is odd.
- Look at house numbers on a walk. In many neighborhoods even numbers are on one side of the street and odd numbers on the other, which children enjoy noticing.
- Play "Fair share": give your child a small pile of crackers to split equally between two people and decide before sharing whether it will come out even.
- Ask "Is it even or odd?" about ages, page numbers and the number of people at dinner, and have your child explain how they know.
Worked examples
These are real questions from the Tutorsaurus even and odd numbers practice, with the answers worked out.
Example 1
Is 8 even or odd?
Choices: Even, Odd
Answer: Even. 8 is even. Look at the ones digit: 8 is even (0, 2, 4, 6, 8).
Example 2
Is 40 even or odd?
Choices: Even, Odd
Answer: Even. 40 is even. Look at the ones digit: 0 is even (0, 2, 4, 6, 8).
Example 3
Is 91 even or odd?
Choices: Even, Odd
Answer: Odd. 91 is odd. Look at the ones digit: 1 is odd (1, 3, 5, 7, 9).