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

For a $0.125 \cdot g$ dose, $2.5 \cdot m L$ of the suspension must be administered.
$1 \cdot m g$ $=$ $1 \times {10}^{-} 3 \cdot g$, likewise $1000 \cdot m g$ $\equiv$ $1.000 \cdot g$
We want a $250 \cdot m g$ or $0.250 \cdot g$ dose, and thus for a concentration of $\frac{250 \cdot m g}{5 \cdot m {L}^{-} 1} = 50 \cdot m g \cdot m {L}^{-} 1$, we require $2.5 \cdot m L$ of the suspension.