Aptitude - Problems on Trains - Discussion

Let the speed of train be x m/s, & the distance be y m; here, 4.5km/hr = 1.25m/s and 5.4km/hr=1.5m/s.

Aaccording to question, y/(x-1.25)=8.4, y=8.4x-10.5 ----(i)
Again, y/(x-1.5)=5.4, y=5.4x-8.1 ----(ii)

Solving (i) & (ii), x =22.5 Ans: 22.5 m/s.

Thank you @Sathees.

Let be considered x is a length, y is a speed, p1 and p2 both represent the person.

Step 1 : p1, p2 speed given for km/hr, Time is given for seconds so km/hr convert to m/s.


P1 => 4.5 * 5/18 = 1.25 m/sec and,

p2 => 5.4 * 5/18 = 1.5 m/sec.

Step 2 : Length or distance (m) = (train speed - person speed) m/sec * time.

x = (y - 1.25) * 8.4,

=> x = 8.4 y - 10.5,

=> 8.4 y - x = 10.5,

x = (y - 1.5) * 8. 5,

=> x = 8.5 y - 12.75,

=> 8. 5 y - x = 12.75.

Step 3:

8.5 y - x = 12.75

8.4 y - x = 10.5
----------------------
0.1 y = 2.25
----------------------

=> y = 22.5 m/sec.


Step 4 : m/sec convert into km/hr (ans is given for km /hr).

y = 22.5 * 5/18

= 4.5 * 18

= 81.0 km/hr.

In the answer, x is distance because speed * time, how come you say that x is speed?

How 2.25 came? Please tell me.

@Saurav 5/18 is the common unit to convert speed by km/hr to m/s. But the question is distance calculated can't be equal because both the persons having different speed and most probably they can't be at the equal level or abreast.

Can anybody tell me the shortcut method because in entrance exam there is not much time to make and solve equations?

Why you take 5/18?

Can anyone explain the first step?

= 4.5 km/hr = 4.5*5/18.

If trains are in same direction the speed should be subtracted otherwise add.