Simple formulae

In a nutshell

Formulae are rules or facts that are written in a mathematical way. They are used to help you work out missing numbers by using other connected quantities.

Understanding and using formulae

When a formula is written out you will see letters or sentences used instead of numbers. These are then replaced by numbers to solve the problem.

Using sentences in formulae

In some cases word problems can be turned into formulae made from sentences.

Example 1 The time needed to cook a cake is forty minutes plus twenty minutes for every egg used. Written as a formula: Cooking time $$= 40$$ minutes $$+ \ (20\ \times$$ number of eggs used)

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Using letters in formulae

In other cases letters might be used to represent quantities. To work out volume, the formula used is: 

volume $$=$$​ length $$\times$$​ width $$\times$$ height. 

This can also be written as:

volume $$=lwh$$​ 

Note: In maths, letters and numbers written next to each other means they are multiplied.

Example 2 What is the volume of this cuboid? Write down the formula: volume $$=lwh$$​  length$$=5cm$$, width$$=2cm$$ and height$$=3cm$$​  $$l=5cm, w=2cm, h=3cm$$​,  Substituting into the formula. volume $$= 5cm \times 2cm \times 3cm = \underline{30cm}$$