Any integer that cannot be divided exactly by 2 is called an odd number. The last digit of an odd number is always 1, 3, 5, 7 or 9.

Now let?s review some rules when adding and subtracting odd and even numbers. When we add or subtract odd or even numbers, the results always follow the following rules:

1.      For Even + Even, the result is Even. For example, 2 + 4 = 6

2.      For Even + Odd, the result is Odd. For example, 6 + 3 = 9

3.      For Odd + Even, the result is Odd. For example, 5 + 12 = 17

4.      For Odd + Odd, the result is Even. For example, 3 + 5 = 8

Remember: the above rules are also the same for subtraction, not just for addition.

Now let?s review some rules when multiplying odd and even numbers. When we multiply odd or even numbers, the results always follow the following rules:

1.      For Even x Even, the result is Even. For example, 2 x 4 = 8

2.      For Even x Odd, the result is Even. For example, 6 x 3 = 18

3.      For Odd x Even, the result is Even. For example, 5 +x 6 = 30

4.      For Odd x Odd, the result is Odd. For example, 3 x 5 = 15