A pot is filled with alcohal. 80% of alcohal is replaced by the same quantity of water. This process is done three times. Find the percentage of alcohal in this mixture of alcohal and water.

Let quantity of alcohal = 1000 L
Quantity of alcohal after 1st process = 80% of 1000 L = 800 L
Quantity of alcohol after 2nd process = 80% of 800 L = 640 L
Quantity of alcohol after 3rd process = 80% of 640 L = 512 L
∴ Required percentage = (512/1000) x 100 = 51.2%