A can build a wall in 15 days, and B can destroy it in 20 days. If they work on alternate days starting with A, in how many days will the wall be built? MCQ with Answer and Explanation
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Question #1
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A and B work together. A alone can complete the work in 30 days and B alone in 28 days. What percentage of the total daily work is contributed by A?
Correct Answer: Option C
Explanation:
A share = (1/30) / (1/30+1/28) ×100 = 48.28%.
A share = (1/30) / (1/30+1/28) ×100 = 48.28%.
This question belongs to:
Maths
Time and Work
Question #2
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A, B and C can do a work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?
Correct Answer: Option A
Explanation:
Total work = LCM(20, 30, 60) = 60 units. Efficiency of A = 3, B = 2, C = 1. Day 1: A works (3 units). Day 2: A works (3 units). Day 3: A, B, and C work together (3 + 2 + 1 = 6 units). Total work in 3 days = 3 + 3 + 6 = 12 units. To complete 60 units, number of 3-day cycles needed = 60 / 12 = 5 cycles. Total days = 5 * 3 = 15 days.
Total work = LCM(20, 30, 60) = 60 units. Efficiency of A = 3, B = 2, C = 1. Day 1: A works (3 units). Day 2: A works (3 units). Day 3: A, B, and C work together (3 + 2 + 1 = 6 units). Total work in 3 days = 3 + 3 + 6 = 12 units. To complete 60 units, number of 3-day cycles needed = 60 / 12 = 5 cycles. Total days = 5 * 3 = 15 days.
This question belongs to:
Maths
Time and Work
Question #3
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A can complete a work in 10 days and B can complete the same work in 30 days. If they work together, in how many days will the work be completed?
Correct Answer: Option B
Explanation:
Combined rate = 1/10 + 1/30. Time = 1 ÷ combined rate = 7.5 days.
Combined rate = 1/10 + 1/30. Time = 1 ÷ combined rate = 7.5 days.
This question belongs to:
Maths
Time and Work
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