Increase and decrease by percentage

To increase an amount by a percentage, find the percentage to increase/decrease by, then add/subtract it from the amount.

Increase by Percentage

To increase 50 by $20\mathrm{\%}$

Find $20\mathrm{\%}$ of 50.

$$10\mathrm{\%}\text{ of }50=50÷10=5$$

$$20\mathrm{\%}\text{ of }50=5\times 2=10$$

Add this to the original amount (the 50).

$$50+10=60$$

Decrease by Percentage

To decrease 80 by $25\mathrm{\%}$

Find $25\mathrm{\%}$ of 50.

$$25\mathrm{\%}\text{ of }80=80÷4=20$$

Subtract this from the original amount (the 80).

$$80-20=60$$