A 60litres solution of alcohol and water contains 20liters of alcohol. how much alcohol must be added to produce a solution of 50% alcohol

Total quantity of solution containing alcohol and water = 60 liters

Amount of alcohol in the solution = 20 liters

Percentage of alcohol in the solution = (20/60) * 100

= 100/3

= 33.33 percent

So

33.33 percent alcohol is = 20 liters

Then

50 percent alcohol = [20 / (100/3) ] * 50

= [ (20 * 3) / 100] * 50

= (60 * 50) / 100

= 3000/100

= 30 liters

So 30 liters of alcohol should be added to make the percentage of alcohol 50% in the solution.