Writing Expressions and Formulae
An expression describes a calculation in letters; a formula links an expression to a result with an equals sign.
An expression is a mathematical phrase that can contain numbers, letters, and operations but has no equals sign. For example, is an expression.
A formula links two or more variables with an equals sign. For example, the perimeter of a rectangle is
To write an expression from words, identify the operation words: "sum" means add, "product" means multiply, "difference" means subtract, and "quotient" means divide. Translate each part step by step.
Type an expression or formula to see its structure. Try the perimeter formula above, or make up your own.
Watch it work
Question: A cinema charges £8 per adult and £5 per child. Write a formula for the total cost for adults and children.
Step 1: Cost for adults: .
Step 2: Cost for children: .
Answer:
Have a go
Q1. Write an expression for "5 more than a number ".
"More than" means add.
Q2. Write an expression for "triple a number then subtract 4".
"Triple" means multiply by 3, then subtract 4.
Q3. A taxi charges a £3 base fare plus £2 per mile. Write a formula for the cost of a journey of miles.
Base fare is 3. Each mile costs 2, so for miles: .
Q4. Write a formula for the area of a triangle with base and height .
Area of a triangle = half of base times height.