posted by DD .
The density of methanol is .7918 g/ml/ How many grams of methanol do I have to add to 35.0ml of water to make a solution containing 25% methanol?
Is that mass percent?
[x grams MeOH/(x g MeOH + 35g H2O)] = 0.25
Solve for x = grams methanol.
Then mass = volume x density. Substitute mass and density and solve for volume.
Post your work if you get stuck.