A and B can complete a piece of work in 20 days and 30 days respectively. If they work on alternate days starting with B, in how many days will the work be finished? MCQ with Answer and Explanation
A and B can complete a piece of work in 20 days and 30 days respectively. If they work on alternate days starting with B, in how many days will the work be finished?
A. 26 days
B. 23 days
C. 25 days
D. 24 days
Answer: Option D
Solution (By JKSSB Mock Tests)
Total work = LCM(20, 30) = 60 units. Efficiency of A = 3, B = 2. In 2 days (B then A), work completed = 2 + 3 = 5 units. Time taken to complete 60 units = (60 / 5) * 2 = 24 days.
A, B and C can do a piece of work in 24, 30 and 40 days respectively. They start together but C leaves 4 days before the completion of the work. In how many days was the work completed?
Explanation:
Total work = LCM(24, 30, 40) = 120 units. Efficiency of A = 5, B = 4, C = 3. Let the total number of days be x. A and B work for x days, while C works for (x - 4) days. 5x + 4x + 3(x - 4) = 120 => 12x - 12 = 120 => 12x = 132 => x = 11 days.
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