Vivek, Dev and Lalit alone can complete a work in 10 days, 15 days and 20 days respectively. In how many days Vivek and Dev together can complete half of the same work?
Let total work to be done = L.C.M. (10,15,20) = 60 units
Vivek complete the work in 10 days, => Vivek's efficiency = $$\frac{60}{10}=6$$ units/day
Similarly, Dev's efficiency = $$\frac{60}{15}=4$$ units/day
=> (Vivek+Dev)'s 1 day's work = $$(6+4)=10$$ units/day
$$\therefore$$ Time taken by them to complete half the work = $$\frac{30}{10}=3$$ days
=> Ans - (C)
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