SOLUTION: A pharmacist wishes to mix a solution that is 5​% Minoxidil. She has on hand 60 ml of a 3​% solution and wishes to add some 7​% solution to obtain the desired 5&

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Question 1071059: A pharmacist wishes to mix a solution that is 5​% Minoxidil. She has on hand 60 ml of a 3​% solution and wishes to add some 7​% solution to obtain the desired 5​% solution. How much 7​% solution should she​ add?
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
v, the amount of the 7% material to use

highlight_green%28%283%2A60%2B7v%29%2F%28v%2B60%29=5%29

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3%2A60%2B7v=5v%2B300
7v-5v=300-180
2v=120
highlight%28v=60%29


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CHECK
%283%2A60%2B7%2A60%29%2F%2860%2B60%29
%28180%2B420%29%2F120
%2818%2B42%29%2F12
60%2F12
5
expected percent as given

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Also notice the given concentrations 3% and 7% for the starting materials. The mixture concentration 5% is in the exact middle of the 3 and 7, so expect to use equal parts of the two starting materials.