Question 321511
Tank contains 60 liters  - 20%
let the amount to be drained be x liters
Balance will be 60-x liters --20%
100% added will be x liters
total will be 60 liters 40%
..
concentration equation
1x+0.2(60-x)=60*0.4
1x+12-0.2x=24
0.8x=12
x=12/0.8
x=15 liters will have to be drained