A jar is filled of liquid which is 3 parts water and 5 parts alcohol. How much of this mixture should be drawn out and replaced such that this mixture may contain half
water and half alcohol?
Answer: B
Let the jar initially contain 8 litres of mixture:3 litres water and 5 litres alcohol
Let x litres of this mixture is drawn out and is replaced by x litres of water.
Amount of water now in the solution: 3-(3/8)x+x.
Amount of alcohol now in the solution: 5-(5/8)x
Desired ratio: 1/1
=>3-(3/8)x+x=5-(5/8)x
x=8/5 litres
%x=((8/5)/8)*100=20%