You need a 55% alcohol solution...

Question

You need a 55% alcohol solution. On hand, you have a 220 mL of a 90% alcohol mixture. How much pure water will you need to add to obtain the desired solution?

You will need

______ mL of pure water

to obtain

 ______mL of the desired 55% solution.

Answer 1

220(.9) + x(0.0) = .55(220+x)

.55x = (.9 -.55)(220) -=.35(220) = 77

x=77/.55 = 140 ml of pure water

mixed with 220 ml of 90% yields

360 ml of 55%

90 is within 35 of 55

0 is within 55 of 55

55/35 = 11/7 = 220/140