A and B together can complete a piece of work in 4 days. If A alone can complete the same work in 12 days, in how many days can B alone complete it? MCQ with Answer and Explanation
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Question #1
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A can do a certain work in the same time in which B and C together can do it. If A and B together could do it in 10 days and C alone in 50 days, then B alone could do it in:
Correct Answer: Option B
Explanation:
Total work = LCM(10, 50) = 50 units. Efficiency of (A + B) = 5, efficiency of C = 1. Total efficiency of (A + B + C) = 5 + 1 = 6. Given A = B + C. So, (B + C) + B + C = 6 => 2(B + C) = 6 => B + C = 3. Since C = 1, B = 2. Time taken by B alone = 50 / 2 = 25 days.
Total work = LCM(10, 50) = 50 units. Efficiency of (A + B) = 5, efficiency of C = 1. Total efficiency of (A + B + C) = 5 + 1 = 6. Given A = B + C. So, (B + C) + B + C = 6 => 2(B + C) = 6 => B + C = 3. Since C = 1, B = 2. Time taken by B alone = 50 / 2 = 25 days.
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Maths
Time and Work
Question #2
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A can finish a work in 12 days and B can do it in 15 days. After A had worked for 3 days, B also joined him to finish the remaining work. In how many days was the remaining work completed?
Correct Answer: Option C
Explanation:
Total work = LCM(12, 15) = 60 units. Efficiency of A = 5, B = 4. In 3 days, A completed 3 * 5 = 15 units. Remaining work = 60 - 15 = 45 units. Combined efficiency of A and B = 5 + 4 = 9 units/day. Time taken for remaining work = 45 / 9 = 5 days.
Total work = LCM(12, 15) = 60 units. Efficiency of A = 5, B = 4. In 3 days, A completed 3 * 5 = 15 units. Remaining work = 60 - 15 = 45 units. Combined efficiency of A and B = 5 + 4 = 9 units/day. Time taken for remaining work = 45 / 9 = 5 days.
This question belongs to:
Maths
Time and Work
Question #3
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A can do a piece of work in 15 days and B in 20 days. They began the work together but A left after 4 days. In how many days will B complete the remaining work?
Correct Answer: Option D
Explanation:
Total work = LCM(15, 20) = 60 units. Efficiency of A = 4, B = 3. Combined efficiency = 7. In 4 days, work completed = 4 * 7 = 28 units. Remaining work = 60 - 28 = 32 units. Time taken by B to complete remaining work = 32 / 3 = 10(2/3) days.
Total work = LCM(15, 20) = 60 units. Efficiency of A = 4, B = 3. Combined efficiency = 7. In 4 days, work completed = 4 * 7 = 28 units. Remaining work = 60 - 28 = 32 units. Time taken by B to complete remaining work = 32 / 3 = 10(2/3) days.
This question belongs to:
Maths
Time and Work
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