What quantity of 70%

Question

What quantity of 70% acid solution must be mixed with a 25% solution to produce 540 mL of a 50% solution?

mL of acid solution =

Answer 1

Let X = quantity of 70% acid  solution, and (540 - X) be the quantity of 25% solution. 

Then take the percentages and multiply them by the volumes to get 

.7 X + .25 (540 - X) = .5 (540)

Simplify collect like terms, and solve for X. 

Answer 2

let x = volume of 70% solution

540 - x = volume of 20% solution

Then just set it up algebraically

C₁V₁ + C₂V₂ = C_fV_f    

0.70x + 0.20(540-x) = 0.5*540

0.70x + 108 - 0.2x = 270

0.5x = 162

x = 324 mL of 70%

and then 540 - x = 216 mL of 20%