Akash are 5 times as efficient as Biplob. Akash can finish the work 60 days earlier than Biplob. If they work individually, how many days would they take to finish the work?

We know,
Speed of Work / Efficiency ∝ 1/Time needed
So more the efficiency, less time is needed to do the task.

Let us denote Akash by 'A' and Biplob by 'B'
Hence,
if A is 5 times faster than B, then B needs 5 times more time than A.
Let A need 'n' days to complete the work.
So B will need 5n days.
Also, 5n – n = 60 ------------------- Given
∴ n = 15 days = Days needed by A to complete work individually
Days needed by B to complete work individually = 5n = 5 x 15 = 75 days.