A pharmacist wishes to mix a solution that is 7​% Minoxidil. She has on hand 90 ml of a 4​% solution and wishes to add some 9​% solution to obtain the desired 7​% solution.

Question

How much 9​% solution should she​ add?

Answer 1

90(.04) + x(.09) = (90+x)(.07)

x(.09 -.07) = 90(.07-.04) = 90(.03) =2.7

.02x = 2.7

x = 2.7/.02 = 270/2 = 135 ml of 9% to get 225 ml of 7%

7-4 =3

9-7 =2

90/135 =10/15=2/3