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. If A, B and C work together, in how many days will they complete the work? MCQ with Answer and Explanation

Explanation:
Combined rate = 1/11 + 1/16. Time = 1 ÷ combined rate = 6.52 days.

Explanation:
Combined rate = 1/11 + 1/21. Time = 1 ÷ combined rate = 7.22 days.

Explanation:
Total work = LCM(10, 15) = 30 units. Efficiency of A = 3, B = 2. In 2 days, A and B do 2 * (3 + 2) = 10 units. Remaining work = 30 - 10 = 20 units. This is completed by B and C in 4 days, so combined efficiency of B and C = 20 / 4 = 5 units/day. Since efficiency of B = 2, efficiency of C = 5 - 2 = 3 units/day. Time taken by C alone = 30 / 3 = 10 days.