Question

you are given a prescription for a hundred mL of a 15% hydrochloric acid solution the pharmacy carries 90% Hydrochloric solution how many mls of the concentration of solutions are needed to fill this prescription

Answer 1

If q represents the quantity of solution needed, you require

... 0.90q = 0.15×(100 mL)

... q = (0.15/0.90)×(100 mL)

... q ≈ 16.7 mL

_____

You actually need 16 2/3 mL of concentrated solution.