Correct Answer - Option 1 : (m-3)/3m days
Given:
Time taken by Arun to dig 1/m part of field = 20 hours
Time taken by Arun and Bhanu both together to dig complete dig = 60 hours
Formula used:
Time = work/efficiency
Calculation:
Efficiency of Arun and Bhanu together = 1/60
Efficiency of Arun = 1/20m
Efficiency of Bhanu = Efficiency of both - Efficiency of Arun = 1\60 - 1/20m = (m-3)/60m
⇒ Bhanu's work in 20 hours = {(m-3) × 20 }/60m = (m-3)/3m
∴ Bhanu alone can did (m-3)/3m work in 20 hours