Inital quantity of water=20 Litres
Inital quantity of milk=80 Litres
Sold Quantity of water =$\frac{20}{4}=5 Litre$
Sold Quantity of milk =$\frac{80}{4}=20 Litre$
Remaining Quantity of water =20-5=15 Litres
Remaining Quantity of milk =80-20=60 Litres
he adds water to replenish the quantity that he has sold.Hence we have to add (5+20)= 25 Litres of water.
Now,
New Quantity of water=15+25=40 Litres
New Quantity of milk=60 Litres
current proportion of water to milk=40:60 = 2:3
Hence, Option(1)2:3 is the correct choice.