Odd and even numbers
An even number can be shared into two equal groups with none left over. An odd number always has one left over. To decide, look only at the last digit (the ones digit).
Key idea / 要点
Even ends in 0, 2, 4, 6 or 8. Odd ends in 1, 3, 5, 7 or 9.
Adding odd and even
There are simple rules when we add them together. If you add two even numbers, or two odd numbers, the answer is always even. If you add one even number and one odd number, the answer is odd. These rules work for small and large numbers, so you never have to guess.
Worked example / 例题
Is 1 234 odd or even? The last digit is 4, and 4 is even, so 1 234 is even. Now check 3 457: it ends in 7, which is odd, so 3 457 is odd.
Remember / 记住
- even + even = even
- odd + odd = even
- even + odd = odd