# A doctor's order is 0.125g of ampicillin. The liquid suspension on hand contains 250 mg/5.0 mL. How many milliliters of the suspension are required?

Jul 10, 2016

$2.5 m L$

#### Explanation:

First lets get the units the same for the suspension (in $m g$) and the required amount of ampicillin (in $g$):

$1 g = 1000 m g \to 0.125 g = 125 m g$

For easy calculation and for better understanding of what you are doing, it is best to then calculate how many $m g$ is in $1 m L$:

$\frac{250 m g}{5.0 m L} = \frac{50 m g}{1 m L}$

So $1 m L$ of the solution contains $50 m g$ ampicillin.
The doctor asks for $125 m g$ of ampicillin which is a volume of:

$\frac{125 \textcolor{red}{\cancel{\textcolor{b l a c k}{m g}}}}{50 \frac{\textcolor{red}{\cancel{\textcolor{b l a c k}{m g}}}}{m L}} = 2.5 m L$

So the required volume of the solution is $2.5 m L$.