A can complete a work in 21 days and B can complete the same work in 31 days. If they work together, in how many days will the work be completed? MCQ with Answer and Explanation
A and B can do a piece of work in 45 and 40 days respectively. They began the work together, but A left after some days and B finished the remaining work in 23 days. After how many days did A leave?
Explanation:
Total work = LCM(45, 40) = 360 units. Efficiency of A = 8, B = 9. B worked alone for 23 days: work done = 23 * 9 = 207 units. Remaining work = 360 - 207 = 153 units. This was done by A and B together. Combined efficiency = 8 + 9 = 17. Number of days they worked together = 153 / 17 = 9 days. Thus, A left after 9 days.
A can do a piece of work in 20 days and B in 30 days. They work together for 7 days and then both leave. Then C alone finishes the remaining work in 10 days. In how many days can C alone finish the full work?
Explanation:
Total work = LCM(20, 30) = 60 units. Efficiency of A = 3, B = 2. Combined efficiency = 5 units/day. In 7 days, work done = 7 * 5 = 35 units. Remaining work = 60 - 35 = 25 units. C takes 10 days to do 25 units, so efficiency of C = 25 / 10 = 2.5 units/day. Time taken by C for full work = 60 / 2.5 = 24 days.
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