Question 15

X alone can do a piece of work in 12 days and Y alone can do the same work in 6 days. In how many days will both together complete the same work?

Solution

Let total work to be done = L.C.M. (12,6) = 12 units

X alone can do the work in 12 days, => X's efficiency = $$\frac{12}{12}=1$$ unit/day

Similarly, Y's efficiency = $$\frac{12}{6}=2$$ units/day

Thus, (X+Y)'s 1 day's work = $$1+2=3$$ units/day

$$\therefore$$ Time taken by them together to finish the work = $$\frac{12}{3}=4$$ days

=> Ans - (B)

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