you start at 20 and count back until you reach 1 (or zero). Each number is one less than the last. You can use number lines like the one below to help you learn how to count on and count back.

When you divide 15 into groups of 5, you make 3 groups. A number line can help you to divide. You count on in steps of the number you want to divide by. Then, count how many steps there are and ...