Time, Speed & Distance
Aptitude

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Q.

A train starts from Delhi at 6:00 am and reaches Ambala cantt. at 10am. The other train starts from Ambala cantt. at 8am and reached Delhi at 11:30 am, If the distance between Delhi and Ambala cantt is 200 km, then at what time did the two trains meet each other?

 A.

8:46 am

 B.

8:30 am

 C.

8:56 am

 D.

8:50 am

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Solution:
Option(C) is correct

Average speed of train leaving Delhi = \(\dfrac{200}{4}=50\) km/hr

Average speed of train leaving Ambala cantt. = \(200\times \dfrac{2}{7}=\dfrac{400}{7}\)

By the time the other train starts from Ambala cantt, the first train had travelled 100 km

Therefore, the trains meet after:

\(=\dfrac{200-100}{(50+400/7)}=\dfrac{14}{15}\)hr

\(=\dfrac{14}{15}\times 60=56\)minutes

Hence they meet at 8:56 am


(5) Comment(s)


Suraj
 ()

Why do we multiply second train by 2/7?


Sirisha
 ()

400/3.5=400*2/7.......,where 3.5 is the time difference between 8am and & 11.30 am


Nairuti Suradkar
 ()

Let t be the start time

A starts at t, while B starts at (t-2)

total distance covered is 200 km

as they are travelling in opposite direction,

relative dist covered

i,e 200=((200/4)*t )+((400/7)*(t-2))

t=176min

i.e 2hrs 56min from start (6 am)

therefore they meet at 8.56am.



Pree
 ()

$=\dfrac{100}{(50+400/7)}$

$=\dfrac{14}{15}$

and

$\dfrac{14}{15} \times 60 =56$


Deepak
 ()

Thanks Pree for the input, corrected now.