How_To_Be_Good_At_Math

CALCULATING • MULTIPLYING BY MULTIPLES OF 10 109

Multiplying by

multiples of 10

To make multiplication calculations involving multiples

of 10 easier, you can combine what you know about the

multiplication tables with what you know about multiplying by 10.

Let’s write 20 as 2 × 10, because

multiplying by 2 and 10

are easier than multiplying by 20.

Look at this calculation. We want to

multiply 126 by 20. It looks tricky, but

it’s simple if you know your multiples of 10.

Now we can multiply 126 by 2.

We know that 26 × 2 = 52, so we

can work out that 126 × 2 = 252

Finally, we just have to multiply 252

by 10. The answer is 2520.

So, 126 × 20 = 2520

Trickier tens

Look at these calculations. Can you

break down the multiples of 10 to

make each calculation simpler and

work out the answer?

25 × 50 =?

0.5 × 60 =?

231 × 30 =?

0.03 × 90 =?

43 × 70 =?

824 × 20 =?

TRY IT OUT

Answers on page 319

To multiply a number by

a multiple of 10, break

the multiple into 10 and

its other factor and do

the calculation in steps.

126 × 2 × 10

252 × 10 = 2520

126 × 2 = 252

126 × 20 =?

126 × 20 = 2520

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