P and Q can do a project in 25 and 50 days respectively. In how many days can they complete 18% of the project if they work together?

Let total work to be done = 50 units

P can complete the work alone in 25 days

=> P's efficiency = $$\frac{50}{25} = 2$$ units/day

Q can complete the work alone in 50 days

=> Q's efficiency = $$\frac{50}{50} = 1$$ unit/day

(P + Q)'s 1 day's work = 2 + 1 = 3 units/day

=> 18% of the work = $$\frac{18}{100} \times 50 = 9$$ units

$$\therefore$$ Time taken by them together to complete 18% of the work = $$\frac{9}{3} = 3$$ days

=> Ans - (B)