Question

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?

Answer 1

`2.5 mL`

Explanation:

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

`1 g = 1000 mg -> 0.125 g = 125 mg`

For easy calculation and for better understanding of what you are doing, it is best to then calculate how many `mg` is in `1 mL`:

`(250 mg) / (5.0 mL)= (50 mg)/(1 mL)`

So `1 mL` of the solution contains `50 mg` ampicillin.
The doctor asks for `125 mg` of ampicillin which is a volume of:

`(125color(red)(cancel(color(black)(mg)))) / (50 (color(red)cancelcolor(black)(mg))/(mL)) = 2.5 mL`

So the required volume of the solution is `2.5 mL`.