Question 164107
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%.