Aptitude - Problems on Trains - Discussion

x - 5 = 45
x= 45+5
x = 50 km/hr.

relative speed when two movable things whose speeds x,y are moving in same direction is =X-Y,
relative speed when two movable things whose speeds x,y are moving in OPPOSITE direction is =X+Y
Its an standard formula

5/18 is conversion of km/hr to m/s and 18/5 is conversion digit m/s to km/s

DONT WORRY FRIENDS ITS VERY SIMPLE

instead of going for a new formula.we can simply get the answer by using the standard formula.i,e

t=(a+b)/(u-v)
u can see this formula from the general formulas of this exercise.
where
t-time taken by the train to cross the man=10 sec;

a-length of the train=125meters;
b=0(because the train is supposed to cross a person);
u=speed of the train(you are supposed to find out);
v=speed of the man who is running=5km/hr=5*(5/18)=25/18m/sec;

by substituting the values in the above equation you can get the value..

Nice explanation friends. !

Both (train and man) moves in same direction so we subtract.

Both moves in opposite direction means we add it.

We convert m into km, sec into hour so we multiply 18/5.

Thanks to all.

I got many idea's to solve this problem.

speed=distance/time.so speed=125/10.....25/2*18/5=45... the question is same direction=x-5=45 x=50

Why 125 is divided by 10?

@kumar
cause speed=distance/time