A and B can complete a work in 10 days and 15 days respectively. They started together, but A left after some days and B finished the remaining work in 5 days. After how many days did A leave? MCQ with Answer and Explanation

Explanation:
Total work = LCM(12, 16) = 48 units. Efficiency of A = 4, B = 3. Combined efficiency = 7 units/day. In 3 days, work completed = 3 * 7 = 21 units. Remaining work = 48 - 21 = 27 units. Time taken by B to complete remaining work = 27 / 3 = 9 days.

Explanation:
Using M1 * D1 = M2 * D2: 10 * 12 = M2 * 8 => 120 = 8 * M2 => M2 = 15 men. More men required = 15 - 10 = 5.

Explanation:
Total work = LCM(20, 30) = 60 units. Efficiency of A = +3, B = -2. In 2 days (A then B), net work done = 3 - 2 = 1 unit. We need to reach 60 units. Since A can add 3 units on his turn, we find when work reaches 60 - 3 = 57 units. 57 units will be done in 57 * 2 = 114 days. On the 115th day, A works and completes 3 units, making the total work 57 + 3 = 60 units. So, the wall is built in 115 days.