Percent Increase and Decrease: Practice

The amount of change is the new value minus the original value.

$\text{change} = 60 - 50 = 10$

The price went up, so this is an increase of $10$ dollars.

The change is $25 - 20 = 5$. Ask what percent $5$ is of the original $20$.

$\frac{5}{20} \times 100\% = 0.25 \times 100\% = 25\%$

So this is a $25\%$ increase.

The change is $13 - 10 = 3$. Compare it to the original $10$.

$\frac{3}{10} \times 100\% = 30\%$

So the quantity rose by $30\%$.

A $10\%$ increase keeps the whole original ($100\%$) and adds $10\%$ more.

$1 + \frac{10}{100} = 1.10$

So you multiply by $1.10$.

Decreasing by $10\%$ leaves the part that remains, which is $100\% - 10\% = 90\%$.

$1 - \frac{10}{100} = 0.90$

So you multiply by $0.90$.

A $25\%$ decrease leaves $100\% - 25\% = 75\%$, so multiply by $0.75$.

$0.75 \times 80 = 60$

So the new value is $60$.

A discount of $50\%$ removes half, so you pay the half that is left.

$100\% - 50\% = 50\%$

You pay $50\%$ of the original price.

A tip is added on, so you pay $100\% + 20\% = 120\%$ of the bill. Multiply by $1.20$.

$1.20 \times 100 = 120$

The total is $120$ dollars.

The size of the change is $50 - 40 = 10$. Compare it to the original $50$.

$\frac{10}{50} \times 100\% = 20\%$

So the value dropped by $20\%$.

A $50\%$ increase keeps the original and adds half of it, so multiply by $1.50$.

$1.50 \times 60 = 90$

So the new value is $90$.

A $20\%$ discount removes $20\%$, so you pay what is left.

$100\% - 20\% = 80\%$

You pay $80\%$ of the original price.

The change is $24 - 20 = 4$. Compare it to the original $20$.

$\frac{4}{20} \times 100\% = 20\%$

So the temperature rose by $20\%$.