5 = .1t
multiply by ten to find how many liters are in the total mix
so they normally have a total of 50 liters. The total mix is the sum of the acetone and the water so 5+w=50 then w = 50-5 then w=45. So they normally ad 45 liters of water to 5 liters of acetone to get a mix of 10% acetone.
However, this time they added 10 liters instead of 5. But they want it to still equal 10% of the total mix, so using the same concept 10=.1t then 100=t. So this new mix must have 100 liters. 100 liters minus 10 liters of acetone is 90 liters. 90 liters minus the initial 45 liters of water is 45 liters. So they must add an additional 45 liters of water to get a mixture of 10% acetone.