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 \(20\%\)

Find \(20\%\) of 50.

\[10\% \text{ of } 50 = 50 \div 10 = 5\]

\[20\% \text{ of } 50 = 5 \times 2 = 10\]

Add this to the original amount (the 50).

\[50 + 10 = 60\]

Decrease by Percentage

To decrease 80 by \(25\%\)

Find \(25\%\) of 50.

\[25\% \text{ of } 80 = 80 \div 4 = 20\]

Subtract this from the original amount (the 80).

\[80 - 20 = 60\]