SOLUTION: How many kilograms of pure alcohol must be added to 40 kg of a 70% alcohol solution to produce an 85% alcohol solution?

Question 164107: How many kilograms of pure alcohol must be added to 40 kg of a 70% alcohol solution to produce an 85% alcohol solution?
Answer by rcmcc(152) (Show Source): You can put this solution on YOUR website!
To solve this question you must first find the quantity of liquid that is not alcohol in the first solution.
Because the 40kg solution is 70% alcohol 30% of the solution is a fixed variable.
30% of 40kg = 12kg.

The second solution is 85% alcohol. Because we can not change the fixed variable the 15% of the new solution weighs 12kg
if 15% of the new solution weigs 12kg then the entire solution weighs 80kg.
because your original solution weighs 40kg, and your new solution weighs 80kg, you would need 40kg of pure alcohol added to the old solution to increase the concentration from 70% to 85%.
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