Both A and B together can complete a work in 20 days and B alone can complete the same work in 36 days. In how many days will A alone complete the work?
Let the total work to be done = L.C.M. (20,36) = 180 units
B alone can complete the same work in 36 days, => B's efficiency = $$\frac{180}{36}=5$$ units/day
Similarly, (A+B)'s 1 day's work = $$\frac{180}{20}=9$$ units/day
=> A's efficiency = $$9-5=4$$ units/day
$$\therefore$$ Time taken by A to complete the work alone = $$\frac{180}{4}=45$$ days
=> Ans - (C)
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