'Arun' alone can complete 60% of the work in 15 days,

Solution

Time taken by 'Arun' alone to complete the work = (15/0.6) = 25 days Time taken by 'Arun' and 'Bhaskar' together to finish the work = (7.5/0.80) = (75/8) days Let, the total work be LCM of [25 and 75] = 75 units So, the efficiency of 'Arun' = (75/25) = 3 units/day Sum of efficiencies of 'Arun' and 'Bhaskar' together = [75/(75/8) ] = 8 units/day So, the efficiency 'Bhaskar' = 8 - 3 = 5 units/day Time taken by 'Bhaskar' alone to finish the work = (75/5) = 15 days