Even numbers can be divided by 2 exactly, with nothing left over: 2, 4, 6, 8, 10. Odd numbers leave a remainder of 1 when divided by 2: 1, 3, 5, 7, 9.
An easy way to tell: look at the last digit. If it's 0, 2, 4, 6, or 8, the number is even. If it's 1, 3, 5, 7, or 9, it's odd. Example: 24 is even because it ends in 4, and 37 is odd because it ends in 7.
We can also check by grouping objects into pairs: if we arrange 6 apples into pairs (two, two, two), nothing is left over, so it's even. But if we arrange 7 apples, one is left alone, so it's odd.
