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06/10/2017 - Multiplication Hacks

Multiplication Hacks

In today's lesson, we have been revisiting the properties of multiplication, so that we can calculate using the most efficient method, (which does not always require a written method.)

Using our times tables

When our knowledge and instant recall of multiplication facts are secure, we can then work out other calculations.

Therefore, if we know :                                                      4 x 6 = 24

We also know that:                6 x 4 = 24          60 x 4 = 240          400 x 6 = 2400     0.4 x 600 = 240

Commutativity

It does not matter the order we put the numbers when we calculate because both ways we will get the same result.

Factorise and multiply

Keeping in mind multiplication's property of associativity, we factorised two digit numbers and then multiplied them in any order. This way, by choosing our methods carefully, we could do some larger calculations mentally.

45 x 25

45 = 9 x 5          24 = 12 x 2

5 x 2 = 10

9 x 12 = 108

108 x 10 = 1080

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