A formula is a rule or equation used to calculate the value of a quantity.
The plural of formula is formulae or formulas.
There are all types of formulae for calculating various quantities in many areas of life.
The subject of a formula is the term which is often on its own on the left hand side.
e.g. For the cost of pizzas formula above the subject of the formula is C
Substitution into a Formula
To find the value of a quantity in a formula we put given values into a formula in place of the variables (written as letters).
e.g. A = lw is the formula for finding the area of a rectangle.
If l = 5 cm and w = 7 cm
A = 5 × 7 cm2
A = 35 cm2