Video: Finding a Missing Number in a Given Mathematical Equation

Complete: (28 ÷ 4) = 2 + _.

02:58

Video Transcript

Complete, 28 divided by four equals two plus what?

Here we have two statements either side of an equal sign. The first statement is a division, 28 divided by four. And, on the right-hand side of the equal sign, we have an addition, two plus what? We don’t know what this missing number is, but we do have something that can help us. And, that’s the symbol in the middle of the two expressions. The equal sign tells us that the expression on the left has an equal value, is exactly the same, as the expression on the right. They’re may be written using different symbols, but they’re still worth exactly the same.

We can imagine a set of balances or weighing scales. On the left, we have 28 divided by four, and on the right, we have two plus something. And, that equal sign in the middle tells us our weighing scales are balanced. So, to find out what our missing number is, we first need to find out the value of 28 divided by four. This will help us. How many fours are there in 28? Let’s count in fours to find out. Four, eight, 12, 16, 20, 24, and 28. That’s seven lots of four in 28. So, we know that 28 divided by four equals seven.

Let’s change the expression on the left-hand side of the equal sign to what it’s worth, which is seven. Now, because we’ve got an equal sign in between both expressions, we know the expression on the right-hand side is going to be worth seven. But, what do we add to two to make seven? Seven is equal to two plus what? Well, we know that we can break seven up into two and five. So, we know the addition on the right-hand side of the equal sign must be two plus five.

First, we calculated 28 divided by four, and we found that that was worth seven. We knew that the equal sign was telling us that 28 divided by four, or seven, was the same as two add something. And, all we had to do was work out what we added to two to make seven. 28 divided by four is equal to two plus five. The missing number is five.

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