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Question

A and B can together complete a task in 18 hours. After 6 hours A leaves. B takes 36 hours to finish rest of the task. How many hours would A have taken to do the task if he worked alone?

A 54 Correct Answer Incorrect Answer
B 45 Correct Answer Incorrect Answer
C 21 Correct Answer Incorrect Answer
D 27 Correct Answer Incorrect Answer

Solution

Let the total number of units of work =108 A and B can do in 18 hours so 108/18 =6 units each hour they both can do 6 units For 6 hours they both worked and so 36 units is done so 108-36=72 units of work is done by B alone in 36 hours I.e 72/36 = 2 units per day Therefore a+b=6 a=6-2 a=4 units per day If A worked alone then 108/4 =27 hours

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