Using 75% solution and pure water to find the desired 75% solution

Question

You need a 75% alcohol solution. On hand, you have a 750 mL of a 95% alcohol mixture. How much pure water will you need to add to obtain the desired solution?

Answer 1

750(.95) + x(0.00) = (750+x)(.75)

712.5 + 0 = 562.5 + .75x

.75x = 712.5- 562.5

.75x = 150

x = 150(4/3)

x = 200 mL of pure water mixed with 750 mL of 95% to get 950 mL of 75% solution

water is 0% which is within 75 of 75%

95% is within 20 of 75%

so you'll need 75/20 = 15/4 = 3.75 times as much 95% as 0% water to get 75%

3.75 x 200 = 750

Answer 2

75% alcohol is 25% water

95% alcohol is 5% water

0.05(750) + 1.00x = 0.25(750 + x)

Can you solve for x and answer?