# Easy Time, Speed & Distance Solved QuestionAptitude Discussion

 Q. A train leaves station $X$ at 5am and reaches station $Y$ at 9 am. Another train leaves station $Y$ at 7 am and reaches station $X$ at 10:30 am. At what time do the two trains cross each other?
 ✖ A. 7:36 am ✔ B. 7:56 am ✖ C. 8:36 am ✖ D. 7:56 am

Solution:
Option(B) is correct

Let the distance between $X$ and $Y$ is $d$ km

Then, speed of $A$ is $\dfrac{d}{4}$ km/hr and that of $B$ is $\dfrac{2d}{7}$ km/hr.

$X$ ------------------- $Y$ ($XY$ = $d$ km)

Relative speed = $\dfrac{d}{4}+\dfrac{2d}{7}=\dfrac{15d}{28}$km/hr

Now distance between these trains at 7 am $=d-\dfrac{d}{2}=\dfrac{d}{2}$ km

Hence, time = $\dfrac{d/2}{15d/28}=\dfrac{14}{15}\times 60=56$

Hence both of them meet at 7:56 am

## (1) Comment(s)

Kalyan
()

in this why we find out relative speed. i con't understand it