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Mental Maths Workbook - techniques to multiply a two digit number by a single digit

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Multipying a two-digit number with a single digit - here are the tricks.

Let us say you want to multiply:

x

We can break the problem into two simpler multiplications and one addition, like this:

x

Alternatively, we could have broken the problem into two simpler multiplications and one subtraction, like this:

x

We can extend this technique to multiplying a three-digit number by a one-digit number, as shown in the following example

x

Splitting the problem as above makes the multiplication simpler because of two reasons:

Note that these techniques work because of the distributive law on multiplication. The distributive law of multiplication states that (a + b) * c = a * c + b * c

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