How many cups of pure water would be mixed with 1.5 cups of a 30% acid solution to dilute into a 4% solution? = _____ cups (answer in decimal or integer form)
1.5 cups of a 30% acid solution contain 1.5 x 0.3 = 0.45 units of acid
Suppose we add x cups of pure water to make up the 4% solution
Then quantity = 1.5 + x cups and the acid content would be (1.5 + x) * 0.04
This should equal 0.45 units of acid that we had earlier
So (1.5 + x) * 0.04 = 0.45
(1.5 + x) * 4 = 45 (after multiplying both sides by 100)
6 + 4x = 45
4x = 45 -6 = 39
x = 39/4 = 9 3/4 or 9.75 cups
Answer: 9.75 cups of pure water must be added
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