Video: Finding the Divisor of a Number given the Quotient as the Subtraction of Two Numbers

Complete: 25 ÷ _ = 7 − 2

02:38

Video Transcript

Complete 25 divided by what equals seven take away two.

Often when we write a number sentence, we’ll have a calculation on one side and a number on the other. But on both sides of the equal sign in this calculation, there isn’t a number at all. There are a two different operations. On the left, we have 25 divided by something. This is the missing number that we need to complete. And on the right-hand side, we have a subtraction, seven take away two. And this equal sign in the centre gives us a clue about how to find the answer.

We know that whatever expressions we can see on either side of the equal sign, they’re both worth the same. We can think of our equal sign as being a little bit like a set of weighing scales or balances. And the equal sign tells us that both sides are balanced. So, what are they both worth? Well, at the moment, we can’t work out the expression on the left-hand side because we’ve got a missing number. But we can work out the expression on the right-hand side.

We know that seven take away two equals five. And because there’s an equal sign in-between both expressions, we also know that 25 divided by something will also equal five. Both sides must be equal. So, now, we can use this to help us find the missing number. What do we divide 25 by to leave us with an answer of five?

Now, we can look at this calculation another way by swapping our missing number and the number five around. In other words, 25 divided by five will help us find our missing number. This will show us the number of fives there are in 25. Let’s count in fives to see how many fives there are in 25. There’s one lot of five in five, two fives in 10. There are three fives in 15, four fives in 20. And so, we know there are five fives in 25.

We know our missing number must be five. Because there are five lots of five in 25, if we divide 25 by five, we get the answer five. And This is the same as seven take away two. 25 divided by five equals seven take away two. Our missing number is five.

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