## Elementary Algebra

To find out how many gallons are in 7 quarts of milk, we multiply 7 by the ratio that converts quarts to gallons. This ratio is $\frac{0.25\ gallon}{1\ quart}$. After all, when multiplied by the original expression, this ratio cancels our the undesired units and leaves us with the desired units, gallons So, 7 quarts $\times$ $\frac{0.25\ gallon}{1\ quart}$ = 7 $\times$ 0.25 = 1.75 gallons