Question 156986
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.