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Maths

Maths

Mental maths strategies

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Mental maths strategies

In a nutshell

Mental calculations can be performed faster by reorganising calculations into an easier format.



Commutative property

The commutative property means that the order in which you multiply or add numbers will have no effect on the answer. 


Example 1

Demonstrate the commutative law with 4×34 \times 3 .


Calculate 4×34 \times 3.

4×3=12 4\times 3 = 12

Reorder the numbers to 3×43 \times4.

3×4=123 \times 4 =\underline{12}​​

Note: The commutative property can be applied even if there are more than two numbers being multiplied together.  



Factor pairs

Factor pairs are two whole numbers which multiply to give the original number. Factor pairs can be used to break up a multiplication into easier steps. 


Example 2

How many factor pairs does 1212 have?


Find all the whole numbers which multiply to give 1212.

12×1=126×2=124×3=12{\begin{aligned} {12 \times1 = 12} \\ {6 \times 2=12}\\ {4 \times 3=12} \end{aligned}}


There are 3\underline{3} factor pairs for 1212.


Note: The commutative property means the factor pairs can be written in the opposite order.


Example 3 

Calculate 7×167 \times 16.


1616  can be split into 88 and 22. Use this to work out 7×167 \times 16.


7×8×27 \times 8 \times 2


Multiply the numbers in an order you find easy.


7×8=5656×2=112or7×2=1414×8=112\begin{aligned} 7\times 8 &= 56 \\ 56 \times 2 &= 112 \\ \\ &or \\ \\ 7 \times 2 &= 14 \\ 14 \times 8 &= 112 \end{aligned}​​


Therefore, 7×16=1127 \times 16 = \underline{112}


Note: 77 is a prime number which means its only factor pair is 11 and 77.


Frequently Asked Questions (FAQ)

FAQs

  • Question: What are factor pairs?

    Answer: Factor pairs are two whole numbers which multiply to give the original number.

  • Question: What is the commutative property?

    Answer: The commutative property means that the order in which numbers are multiplied has no effect on the answer.

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