A formula is a mathematical rule that shows the relationship between different variables. A formula can be created and used for something that is calculated frequently.
Part ofMathsExpressions and equations
Use algebra to solve this problem.
A plumber charges £40 for a call out, and an extra £18 for every hour. How long did a job that cost £130 take?
The formula for this plumber's charge is:
\(T = £60 + £20 \times h\) where \(T\) is the total cost and \(h\) is the time in hours.
For this question, the formula will need to be solved to find \(h\).
\(T = £40 + £18 \times h\)
Substitute the total cost as £130.
\(£130 = £40 + £18 \times h\)
First, take £40 from each side.
\(£90 = £18 \times h\)
Next, divide both sides by 18.
\(\frac{£90}{18} = \frac{£18 \times h}{18}\)
\(5 = h\)
Answer: The plumber worked for 5 hours to earn £130 .
