word problems

Question

You need a 90% alcohol solution. On hand, you have a 25 mL of a 45% alcohol mixture. You also have 95% alcohol mixture. How much of the 95% mixture will you need to add to obtain the desired solution?

You will need _____?
mL of the 95% solution

Answer 1

The amount of alcohol in the 45% solution is .45(25) mL.

To this we add x mL of a 95% solution containing .95x mL of alcohol 

We wish to end up with a 90% solution that will have .9(25+x)mL of acohol

 

.45(25) + .95x = .9(25+x)

 

Solve the equation for x to determine the amount of 95% solution needed.