Suppose the capacity of vessel is 120 litres and alcohol is filled in it?
When the vessel got 1/4th empty, it was filled with spirit;
∴ Quantity of alcohol = 120 × 3/4 = 90 litres
⇒ Quantity of spirit = 120 × 1/4 = 30 litres
Again when the vessel got 1/3rd empty, it was filled with alcohol;
∴ Quantity of alcohol = 90 × 2/3 + (120/3) = 60 + 40 = 100 litres
Quantity of spirit = 30 × 2/3 = 20 litres
Again, when the vessel got 1/5th empty, it was filled with spirit;
∴ Quantity of alcohol = 100 × 4/5 = 80 litres
Quantity of spirit = 20 × 4/5 + (120/5) = 16 + 24 = 40 litres
∴ Percentage of spirit in the vessel = [40/120] × 100 = 33.33%