Video: Writing Two Subtraction Sentences to Represent the Same Subtraction Problem

There are 5 carrots. A rabbit eats 3 of them. Which of the following gives the number of carrots left? [A] 3 − 2 = 5 [B] 5 − 2 = 3 [C] 5 = 3 − 2 [D] 5 − 3 = 2 [E] 3 = 5 − 2. Which of the following is another subtraction equation for the number of carrots left? [A] 3 = 5 − 2 [B] 2 = 5 − 3 [C] 5 − 2 = 2 [D] 5 − 2 = 3

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Video Transcript

There are five carrots. A rabbit eats three of them. Which of the following gives the number of carrots left? Three subtract two equals five, five subtract two equals three, five equals three subtract two, five subtract three equals two, or three equals five subtract two. Which of the following is another subtraction equation for the number of carrots left? Three equals five subtract two, two equals five subtract three, five subtract two equals two, or five subtract two equals three.

We’re given lots of subtraction facts to choose from in this question. And did you notice they all sound very similar. That’s because the numbers five, three, and two keep cropping up, don’t they? It could be very easy to get confused with this question, so we’re going to have to read it really carefully. To begin with, we’re told that there are five carrots. Can you see them in the picture? One, two, three, four, five. But these five carrots aren’t around for long because we’re told that a rabbit eats three of them. And we can see these in the picture too, can’t we? These are the carrots that have been crossed out, one, two, three. So, there were five carrots to begin with and a rabbit has eaten three of them.

Our first question asks us, which of the following gives the number of carrots left? Well, first of all, can you see how many carrots are left, one, two. Now, we’re given the five different subtraction facts to choose from, but only one of them is a way of showing what’s happened to these carrots. Let’s try and write down what’s happened as a subtraction fact and then look for a fact that matches what we’ve written.

We were told we had five carrots to start with, so let’s write down the number five. And we also know that a rabbit eats three of them. This is the same as taking away three of them, isn’t it? So, we’re going to write the subtraction symbol and then the number three, five take away three. Now, as we’ve just said, we’ve counted how many carrots are left, and there are two. So, the subtraction that shows us the number of carrots left is five take away three equals two. Now can you see this subtraction fact in the ones that we’re given? Yes, we can. Five take away three equals two.

But there’s another part to this question. We’re asked which of the following is another subtraction equation for the number of carrots left. And we’re asked this question because although we can write five subtract three equals two, there’s another subtraction fact that we can write. This time, let’s go through each subtraction really carefully and try to understand what it’s telling us.

Firstly, three equals five take away two. Now, this is interesting because this subtraction starts with the answer and then we have the subtraction. But what it means is three is what we have left over if we start with five and we take away two. So, we could model this using counters. Here are five counters. And it is correct; three is what’s left over if we start with five and take away two. But it’s not what’s happened to our carrots, is it? The rabbit ate or took away three of them, not two. So, the subtraction we’re looking for is not this one.

The next subtraction says two equals five take away three. This is another calculation that starts with the answer. But if we think about what it means, it’s telling us that two is what’s left if we start with five and take away three. And if we model this with counters, we can see that this is exactly what happens to our carrots. Two carrots are what’s left over if we start with five and take away three. And if we write the subtraction underneath the one we’ve already got at the top, we can see that it’s almost exactly the same. The parts of it are just switched around a little bit. Five take away three equals two. Two equals five take away three.

If there are five carrots and a rabbit eats three of them, we can find out the number of carrots left by working out five take away three equals two. And another way of saying exactly the same thing is two equals five take away three.

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