You need a 55% alcohol solution. On hand, you have a 360 mL of a 40% alcohol mixture. How much pure alcohol will you need to add to obtain the desired solution?

Question

how much ml of pure alchohol and how much ml of the desired 55% solution

Answer 1

The total ml will be 360 + x

after adding x ml of pure alcohol

 

Look at the concentrations of alcohol

(40% of 360 ml)+(100% of x ml) =

(55% of 360+x ml)

 

.4(360) + 1(x) = .55(360 + x)

 

Solving for x tells you how many ml

of pure alcohol to add.  Then 360+x 

is the final total of 55% solution.