X can do a piece of work in 'p' days and Y can do the same work in 'q' days . Then the number of days in which X and Y can together do that work is
Let total work to be done = $$pq$$ units
X can do the work in $$'p'$$ days
=> X's efficiency = $$\frac{pq}{p}=q$$ units/day
Similarly, Y's efficiency = $$\frac{pq}{q}=p$$ units/day
=> (X+Y)'s 1 day's work = $$(p+q)$$ units/day
$$\therefore$$ Number of days in which X and Y can together do that work = $$\frac{pq}{p+q}$$ days
=> Ans - (C)
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