A can complete a work in 21 days and B in 17 days. If they work together, the work will be completed in: MCQ with Answer and Explanation

Explanation:
Combined rate = 1/21 + 1/31. Time = 12.52 days.

Explanation:
Total work = LCM(10, 12, 15) = 60 units. Efficiency of A = 6, B = 5, C = 4. Combined efficiency = 6 + 5 + 4 = 15 units/day. Time taken = 60 / 15 = 4 days.

Explanation:
Efficiency of 5 men = 1/6. Efficiency of 10 women = 1/5, so efficiency of 5 women = 1/10. Combined efficiency of 5 men and 5 women = 1/6 + 1/10 = (5 + 3) / 30 = 8 / 30 = 4 / 15. Time taken together = 15 / 4 = 3.75 days.