A alone can complete a work in = 12 days B alone can complete the same work in = 15 days C alone can complete the same work in = 20 days Formula:
Total work = Efficiency × Time Calculation:
Total work = 60 units (LCM of 12, 15 and 20) ⇒ Efficiency of A = 60/12 = 5 units/day ⇒ Efficiency of B = 60/15 = 4 units/day ⇒ Efficiency of C = 60/20 = 3 units/day 60% of the total work = 60 × 60/100 = 36 units ∴ Time taken by A, B and C to complete 60% of the work = 36/(5 + 4 + 3) = 36/12 = 3 days