SOLUTION: My question is: Minoxidil is a drug that has recently proven to be effective in treating male pattern baldness. Water must be added to 20 mL of a 4% solution to dilute it to a 2%

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Question 159535: My question is:
Minoxidil is a drug that has recently proven to be effective in treating male pattern baldness. Water must be added to 20 mL of a 4% solution to dilute it to a 2% solution. How many milliliters of water should be used? (Hint: Water is 0% minoxidil.) The answer is 20 mL, but I cannot put it into an ordered equation. My mind knows the answer, but I cannot formulate it on paper. This is my first college algebra class and my mind has difficulty with this kind of logic. Please help.

Answer by ptaylor(2198) About Me  (Show Source):
You can put this solution on YOUR website!
Let x=amount of water needed
Now we know that the amount of pure minoxidil in the 20ml of the 4% solution(0.04*20) plus the amount of pure minoxidil in the water (0) has to equal the amount of pure minoxidil in the final mixture(0.02*(20+x)). So our equation to solve is:
0.04*20=0.02(20+x) get rid of parens and simplify
0.8=0.4+0.02x subtract 0.4 from each side
0.8-0.4=0.4-0.4+0.02x collect like terms
0.4=0.02x divide each side by 0.02
x=20 ml -----amount of water needed
Hope this helps---ptaylor