## Elementary Algebra

To find the percentage change, we use the following formula: percentage change = $\frac{New\ amount\ -\ Original\ amount}{Original\ amount}$ $\times$ 100% The original dosage was 40 milligrams. The new dosage is 30 milligrams. We substitute these values into the formula to obtain: percentage change = $\frac{30\ -\ 40}{40}$ $\times$ 100% percentage change = $\frac{-10}{40}$ $\times$ 100% percentage change = -0.25 $\times$ 100% percentage change = -25% Because it is a negative number, it is a percent decrease.