A and B can do a piece of work in 12 days, B and C in 15 days, and C and A in 20 days. In how many days can B alone complete the work? MCQ with Answer and Explanation

Total work = LCM(12, 15, 20) = 60 units. Efficiency of (A+B) = 5, (B+C) = 4, (C+A) = 3. Summing efficiencies gives 2*(A+B+C) = 12 => Efficiency of (A+B+C) = 6. Efficiency of B = (A+B+C) - (C+A) = 6 - 3 = 3. Time taken by B alone = 60 / 3 = 20 days.