A can complete a work in 20 days and B in 40 days. After working together for 5 days, what percentage of work remains? MCQ with Answer and Explanation

Explanation:
Let efficiency of C = 1, then B = 2 and A = 4. Combined efficiency = 1 + 2 + 4 = 7 units/day. Total work = 4 * 7 = 28 units. Time taken by C alone = 28 / 1 = 28 days.

Explanation:
Total work = 12 * 12 = 144 man-days. In 6 days, 12 men complete = 12 * 6 = 72 man-days. Remaining work = 144 - 72 = 72 man-days. Remaining men = 12 - 6 = 6 men. Time taken by 6 men to complete remaining work = 72 / 6 = 12 days.

Explanation:
Combined rate = 1/21 + 1/16. Time = 1 ÷ combined rate = 9.08 days.