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Mental Maths Workbook - multiplication by 9 trick


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Normally, you should know the multiplication tables. However, there is a simple trick that you can use to multiply a single digit number by nine.

Let us say you want to multiply:


A trick is to write down the ten's digit as the multiplicand less 1 and then the second digit will be 10 minus the multiplicand. That is:


And indeed, when you multiply 4 by 9, we get 36.

Please note that this trick works only for single digits.When multiplying a two digit number by 9, we should multiply the number by 10 and then subtract the multiplicand from that number. For example:


And indeed, 522 is the correct result. The above technique works for any number of digits multiplied by 9.

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