Video: Multiplying One-Digit Numbers Using Another Multiplication Sentence

We know that 2 × 9 = 18. Use this to find 4 × 9.

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Video Transcript

We know that two times nine equals 18. Use this to find four times nine.

This question then is asking us to find the answer to four times nine, and we’re told how to do it. We need to use the fact two times nine equals 18 to help. Now, how can we use this first fact to help? What’s the link between two times nine and four times nine? Perhaps you’ll be able to spot the link if we model some arrays. Here’s the fact we know already, and here’s the fact we need to find. It’s double the size, isn’t it? Four is double two. So if we know what two times nine is, and we do, we can just double it to find the answer to four times nine.

So what is 18 doubled? Eight doubled is 16, and 10 doubled is 20. And if we put these two parts together, we get the total 36. We’ve used doubling to help us with our times tables facts. If we know what two times nine is, then we can double it to find four times nine. And that’s how we know four times nine is double 18. The answer is 36.

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