Question Video: Addition and Subtraction of Numbers up to 99 Mathematics • 1st Grade

16 + 3 = 19. Which number sentence is missing from the number sentences 3 + 16 = 19, 16 + 3 = 19, and 19 − 16 = 3?


Video Transcript

16 plus three is 19. Which number sentence is missing from the number sentences three plus 16 equals 19, 16 plus three equals 19, and 19 take away 16 equals three?

It seems from this question that we got a missing number sentence here. We’re given a family of three different number sentences, but there must be a fourth one that we need to find. To begin with, we’re given a number fact. 16 plus three is 19. We know we could model this using cubes. 16 plus three is 19. And if we look at our number sentences that we’re given, the second one shows this number fact written as a number sentence 16 plus three equals 19. Now, we can use these three numbers, 16, three, and 19, to write a family of addition and subtraction facts because 16 and three are two parts that make a whole amount, 19.

And you know, we could make that whole amount in one other way. If we look at our train of cubes, we could just swap the pink and the orange cubes around. Three plus 16 is 19 too. And this is where we get our first number sentence from. So we start off with two additions. Our final number sentence is a subtraction, and we can see the same three numbers again. This time, we’re starting with the whole amount. If we have 19 and we take away 16, we’re left with three. So we have two additions, but we only have one subtraction.

Let’s try and find another subtraction that we could make using these numbers. We know the whole amount is 19. So if we’re going to take away a number, we need to start with this whole amount. Let’s make 19 the first number in our number sentence. And we’re going to look for another subtraction. So we need to use the subtraction symbol. Now, we need to take away one of the parts. In the subtraction we’re already given, we’ve taken away 16. So instead of taking 16, let’s take away three.

19 take away three equals what? Well, we know from that very first number fact that 16 and three go together to make 19. And so if we start with 19 and we take away three, we’re going to be left with 16. We can use one addition fact to write a whole family of addition and subtraction facts. The number sentence that’s missing is 19 take away three equals 16.

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