What is Percentage?

To find a percentage of a quantity, multiply: $x\%$ of $A$ is $\dfrac{x}{100} \times A$. To write one quantity as a percentage of another, divide and multiply by $100$. A percentage change is $\dfrac{\text{new} - \text{old}}{\text{old}} \times 100\%$. An increase of $20\%$ followed by a decrease of $20\%$ does not return to the start, because the second percentage is of a different amount.