Percentages and multipliers

The idea

A multiplier does a percentage change in one step. An increase of $15\%$ is $\times 1.15$, a decrease of $15\%$ is $\times 0.85$.

1. Write the percentage as a decimal and add it to $1$ (or take it from $1$).
2. Multiply the amount by the multiplier.
3. Percentage change $= \frac{\text{change}}{\text{original}} \times 100$.

Watch out Percentage change divides by the original amount, not the new one.