From a container of beer, a thief has stolen15 liters of beer and replaced it with water. He repeated the same process. In three attempts the ratio of beer and water became 343 : 169. The initial amount of beer in the container was:

120 liters

We know that,

Final Quantity = Intital Quantity(1 - replaced/total)ⁿ   (where n = no. of process)

We have,

Thief stolen cold drink at one time = 15 lts

According to the question,

Let the final Quantity and Initial Quantity of cold drink be 343x and 512x

and total Quantity of vessel be y

= 343x = 512x(1 - 15/y)³

= y = 120 litres