Video: Using Repeated Subtraction on Number Lines to Divide by 2

There are 16 flip-flops. How many pairs of flip-flops are there? Hint: Make groups of 2. Use the number line to help you.

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Video Transcript

There are 16 flip-flops. How many pairs of flip-flops are there? Hint: Make groups of two. Use the number line to help you.

We’re shown a group which contains 16 flip-flops. We’re asked to work out how many pairs of flip-flops there are. A pair is equal to two, so a pair of flip-flops is two flip-flops. So the question is asking us how many twos there are in 16? In other words, we have to work out 16 divided by two. This is why the question tells us to make groups of two. We’re also told to use the number line to help us. We can see from the number line that there are pairs of flip-flops.

The number line starts at 16 and takes away two each time. This is because each pair is equal to two flip-flops. So we can see that the first pair takes us from 16 to 14 because 16 take away two is 14. If we take away another two, 14 take away two gives us 12. So we need to keep making pairs of flip-flops and taking away two each time until we reach zero on the number line. Repeated subtraction is the same as division. We’ve already taken away two pairs of flip-flops. If we take away another pair, that takes us to 10. We can keep on taking away two until we reach zero.

Let’s count back in twos from 16. 16, 14, 12, 10, eight, six, four, two, zero. How many jumps of two did we make back on the number line? One, two, three, four, five six, seven, eight. 16 divided by two equals eight. There are eight pairs of flip-flops. We started at 16 on the number line. And we took away eight lots of two.

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