Question 1162819

You need a 35% alcohol solution. On hand, you have a 140 mL of a 65% 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 35% solution.
<pre>Let amount of water to add be W
Percent of water in 65% mixture: 35
Required percent of water in 35% mixture: 65
We then get following: .35(140) + W = .65(140 + W)
                        49 + W = 91 + .65W
                       .35W = 42
Amount of water to add, or {{{highlight_green(matrix(1,6, W, "=", 42/.35, "=", 120, mL))}}}