'A', 'B' and 'C', alone can complete a piece of work

Solution

Let the total work be '60x' units. So, efficiency of 'A' = 60x ÷ 12 = '5x' units/day efficiency of 'B' = 60x ÷ 15 = '4x' units/day efficiency of 'C' = 60x ÷ 20 = '3x' units/day Work done by 'A', 'B' and 'C' together in 4 days = Work done by 'A' alone in 3 days + Work done by 'A', 'B' and 'C' together on 4^th day Work done by 'A', 'B' and 'C' together in 4 days = 5x X 3 + (5x + 4x + 3x) X 1 = 15x + 12x = '27x' units So, Work done by 'A', 'B' and 'C' together in next 4 days = '27x' units Amount of work done in first 8 days = 27x X 2 = '54x' units Remaining work = 60x - 54x = '6x' units So, time taken by 'A' to complete the remaining work = 6x ÷ 5x = 1(1/5) days So, total time taken = 8 + 1(1/5)  = 9(1/5) days