Formulas and rules
Every key math formula and rule, organised by topic and school level, with examples and study tips.
Percentages 4
M2
Percentage of a number
p% of n = (p / 100) x n
A percentage is a fraction out of 100.
M3
Percentage increase and decrease
change% = (new - old) / old x 100
Compare the change to the original amount.
M4
Reverse percentage
original = final / multiplier
To find the original price after a change, divide by the multiplier.
M5
Compound interest
A = P (1 + r)^n
Interest is added to the total each period, so it grows exponentially.