P and Q are 27 km away. Two trains with speed of 24 km/hr and 18 km/hr respectively start simultaneously from P and Q and travel in the same direction. They meet at a point R beyond Q. Distance QR is

Answer: Option B

Relative speed = 24 - 18 = 6 km/hr
Time required by faster train to overtake slower train $$=\frac{27}{6}=4\frac{1}{2}\text{ hr}$$
$$\therefore$$ Distance between Q and R $$=18\times 4\frac{1}{2}=81\text{ km}$$