Interpreting formulae

A formula is an equation that shows the relationship between variables. These variables could be:

  • the cost of hiring a worker based on the number of hours worked
  • the cost of hiring a van based on the number of days it is needed for

A formula can be expressed as a worded problem or as an equation using words or letters.

Example 1

Van hire advert with the text '£40 per day + £100'

Cost of hiring a van = number of days × £40 + £100

This formula allows you to calculate the cost of hiring a van based on the number of days it is needed for.

As you can see, there is a flat charge of £100 no matter how many days it is needed for.

For each day it is needed £40 is added to this cost.

Example 2

Gareth is a electrician. He charges a call-out fee of £45 in addition to £15 for every hour on the job.

This can be re-written as an equation:

Wages = number of hours × £15 + £45.