Answer:
50%
Step-by-step explanation:
This question is solved by C1V1 + C2V2 ÷ V1 + V2 = final concentration
Let x = volume of 70% solution
let's express the concentrations as decimals, so 70% = 0.7, 50% = 0.5, and 40% = 0.4
then 0.7X + 50L.4 ÷ X + 50L = 0.5
this equation becomes 0.5(X + 50) = 0.7X + 20
which yields 0.5X + 25 = 0.7X +20
combining, we get 5 = 0.2X, and 25 = X
when we mix the two volumes, we get 50L x 40% + 25L x 70%,
which yields 20L of 100% alcohol, and 17.5L of 100% alcohol, for a total of 37.5L of alcohol in 75L of solution
which is a final concentration of 50%
