math
posted by Dawn .
how many liters of water must be added to 30 liters of a 20% alcohol solution to dilute it to a 15% solution?

you are diluteing it 20/15=1.333 times
Add one part solution, .333333 water.
This means if one part is 30 liters, add 10 liters water.
Check: .2*30/(40+10)=6/40=.15 or 15 percent.