Video: Subtraction of Numbers up to 999

Complete the diagram by following the arrows.


Video Transcript

Complete the diagram below by following the arrows.

We can tell by looking at the direction of the arrows in this diagram that it has a start point and an end point. We start with the number 900 and follow the line around until we reach this unknown number at the end. In fact, we can see that the diagram contains three unknown numbers. How are we going to know what to fill in?

We’re given three calculations to help us. They’re all subtractions, take away 300, take away 200, and then take away 200 again. All of these numbers are multiples of 100. They’re all hundreds numbers, and this means we subtract a number of 100s every time. So, the number we begin with is 900. And we need to follow the arrow around. And it seems that we need to take away 300 along the way. What happens if we take away three 100s from 900?

We can count back in 100s to find the answer, 100, 200, 300. We’ve subtracted 300 altogether. We know nine take away three equals six. So, 900 take away 300 equals 600. And so, we can fill in our first missing number, 600. Now, we need to start with 600 and continue moving around the diagram. This time we need to take away 200 along the way, 100, 200. We know six take away two equals four. So, 600 take away 200 leaves us with 400. We can now complete our second missing number, 400.

Finally then, we need to start with 400 and follow the diagram around to the end. And this time we also need to take away another lot of 200, 100, 200. Four take away two equals two. And so, 400 take away 200 equals 200. Our final missing number is 200.

We completed the diagram by using our knowledge of subtracting multiples of 100. 900 take away 300 gave us our first missing number, which was 600. Then, 600 take away 200 gave us our second missing number, which was 400. And finally, 400 take away 200 gave us our last missing number, which was 200. The diagram’s missing numbers from left to right are 600, 400, and 200.

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