Skill: Identify odd numbers

An odd number has one left over when you make pairs. In base ten, look at the ones digit:

• $1, 3, 5, 7,$ or $9$ means the number is odd.
• $0, 2, 4, 6,$ or $8$ means the number is even.

Example: Is $27$ odd?

1. Find the ones digit of $27$. It is $7$.
2. Since $7$ is in the odd-number list, $27$ is odd.
3. You can also check by making pairs: $27$ objects make $13$ pairs with $1$ left over.

So, $\boxed{27\text{ is odd}}$.

Remember, $0$ is even because it can be split into pairs with nothing left over.