Correct Answer - Option 2 : 25/9 days
Given:
M is thrice as efficient as N and N is twice as efficient as O.
O alone can complete a piece of work in 25 days.
Concepts used:
Time = Work/Efficiency
1 day work of individual = Work/Time
Calculation:
O alone can complete a piece of work in 25 days.
1 day work of O = 1/25
⇒ The efficiency of O = 1/25
⇒ The efficiency of N = 2 × 1/25
⇒ Efficiency of M = 3 × 2/25 = 6/25
⇒ 1 day work or combined efficiency of M, N and O = (1/25) + (2/25) + (6/25) = 9/25
⇒ Time taken by M, N and O in completing a full piece of work = 25/9 days
∴ M, N and O took 25/9 days to complete the full piece of work.