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Multiplication by 9, 99, 999, etc.One way to multiply a number by 9 is to multiply by 10 and then subtract the number from the product. For example,
The rule is based on the distributive law and applies in other similar situations. For example, to multiply by 99, multiply by 100 and then subtract the number:
To multiply by 999, multiply by 100 and subtract the number from the product:
Copyright © 1996-2008 Alexander Bogomolny |
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