Mandar works 3 times as fast as Samarth. If Samarth can complete a job alone in 28 days, then in how many days can they together finish the job?
Let total work to be done = 28 units
Samarth's efficiency = $$\frac{28}{28} = 1$$ unit/day
Mandar works 3 times as fast as Samarth
=> Mandar's efficiency = $$3 \times 1 = 3$$ units/day
Thus, (Samarth + Mandar)'s 1 day's work = 1 + 3 = 4 units/day
$$\therefore$$ Time taken by them to finish the work together = $$\frac{28}{4} = 7$$ days
=> Ans - (D)
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