Video: The Doubling and Halving Strategy for Multiplication

Victoria knows a strategy to multiply by making easier calculations with the same answer. Use her strategy to find the missing numbers.

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Video Transcript

Victoria knows a strategy to multiply by making easier calculations with the same answer. Using her strategy, find the missing numbers.

Victoria says if you double one number, halve the other. So 18 divided by two equals nine. And five times two equals 10. 18 times five is the same thing as nine times 10. But nine times 10 is a bit easier to calculate mentally.

We’re going to use her strategy to fill in the blanks for the other two questions. If we multiply five times two to get 10, then we need to divide 22 by two. 22 divided by two equals 11. And that means 22 times five will equal 11 times 10.

Following the same procedure, if we multiply 15 times two, we get 30. And since we multiplied 15 by two, we need to divide 12 by two. 12 divided by two equals six. We can say that 15 times 12 equals 30 times six.

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