Question Video: Dividing by 3 Using Counting Back Mathematics • 3rd Grade

Count back to find 15 ÷ 3.

01:51

Video Transcript

Count back to find 15 divided by three.

In this question, we’ve got a division to solve. We need to divide 15 by three. One way of thinking of this is, how many threes are there in 15? And one way we could find out how many threes are in 15 is if we count back, which is what this question tells us to do. We could do this on a number line. So we could start by sketching a number line and labeling zero at one end and 15 at the other. But remember, we’re going to be working backwards, so we’re going to start at 15 and go back toward zero. Now to find out how many threes there are in 15, we could count back in threes. So starting on 15, let’s count back one lot of three. 15, 14, 13, 12.

So we know there’s definitely one lot of three in 15. Let’s take away another lot of three, starting with 12, 11, 10, nine, and another jump of three, starting with nine, eight, seven, six. So we’ve already made three jumps of three and we’ve landed on the number six. Can you see how many more jumps of three we need to make? Six, five, four, three. And then if we take away one more lot of three, it’s going to take us to zero. We’ve made five jumps of three altogether to get from 15 all the way back to zero. This tells us that there are five threes in 15. We’ve used counting backwards or repeated subtraction to help us solve this division. 15 divided by three equals five.

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