A certain drug is made from only two ingredients: compound A and compound B. There are 5 milliliters of compound A used for every 7 milliliters of compound B. If a chemist wants to make 684 milliliters of the drug, how many milliliters of compound A are needed?

There are 5 milliliters of compound A for every 7 milliliters of compound B.

So the ration between compound A and B will be:

A:B = 5:7

Total amount of drug = 684

Therefore, the amount of drug A needed will be:

[tex] \frac{5}{5+7}*684 \\ \\ = \frac{5}{12}*684 \\ \\ =285[/tex]

Therefore, out of 684 milliliters 285 would be the compound A and the rest would be compound B