From the information given, we can write the conversion ratio as,
[tex]\frac{2mg}{1ml}[/tex]We want to know how many mg (let it be "x") is there in 20 ml.
We can setup a proportion as shown below:
[tex]\frac{2mg}{1ml}=\frac{x}{20ml}[/tex]Solving for "x",
[tex]\begin{gathered} \frac{2mg}{1ml}=\frac{x}{20ml} \\ x\times1=2\times20 \\ x=40mg \end{gathered}[/tex]Answer40 mg