SOLUTION: please help me solve this problem: Sarah sells a fruit juice that she makes by mixing together fruit juice concentrate and water. She wants her mixture to contain 30 liters of 15%

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Question 156986: please help me solve this problem:
Sarah sells a fruit juice that she makes by mixing together fruit juice concentrate and water. She wants her mixture to contain 30 liters of 15% strength juice. How much of the fruit juice concentrate will she need if the concentrate contains 90% juice?
Found 2 solutions by nerdybill, gonzo:
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
Let j = amount of juice concentrate
30 - j = amount of water
.
.90j = .15(30)
j = (.15(30))/.90
j = (15(30))/90
j = (15)/3
j = 5 liters (juice concentrate)


Answer by gonzo(654) About Me  (Show Source):
You can put this solution on YOUR website!
she would need 5 liters of .90% juice to provide the needed 15% overall concentration of juice.
5 liters of .90% juice = 4.5 liters of 100% juice concentrate.
4.5 liters of juice / 30 liters total = 15% juice concentration overall.
first i determined how much 100% juice i needed which was 15% times 30 liters and came out to be 4.5 liters.
then i determined how much 90% concentrate i needed to make 4.5 liters of pure juice.
equation was .9 * x = 4.5 liters of juice.
x = 4.5/.9 = 5 liters of 90% concentrate required.