Aptitude - Problems on Trains - Discussion

Distance =speed * time,
D=78km/h*1minute,
D=78*5/18*60.
D=78*.277*60.
D=21.6*60= 1300-800= 500.

I am not getting, how come 5/18? Please, someone explain me.

1km = 1000m,
1hr = 3600sec.

Convert,
Km/hr=m/sec.
= 1000/3600m/sec,
= 5/18m/sec.

Thanks all for explaining the answer.

X+800 = 78 * 5/18 * 60,
X+800 = 13*5/3 *60,
X+800 = 13*5*20,
X+800 = 65*20,
X+800 = 1300,
X = 1300-800,
X = 500.

Why need to convert 1 minute to 60 seconds?

@Agggy.

we add the length of the the train and tunnel because the train is said to have crossed the tunnel if and only if its entire part including the the very last end of it leaves the tunnel.

so if the train has crossed the tunnel in 1min then it would have covered the entire length of the tunnel and a certain distance outside the tunnel (the distance covered by the train until the very last end of the train leaves the tunnel).

So,
that 'certain distance' = length of the train.
.A______x______.B.______800______.C.

where x is the length of the tunnel and the length of the train is 800 m.
the total distance covered by the train is x + 800.

DISTANCE = X+800 m
SPEED = 78 km/hr
TIME = 60sec.

convert speed from km/hr to m/s.
SPEED = 78x1000/60 x 60.
SPEED = 65m/s.

distance /speed = time.
X + 800/65 = 60,
X + 800 = 60x65/3,
X + 800 = 3900/3,
X + 800 = 1300,
X = 1300 - 800,
X = 500.

3(800+x) = 1900
2400+3x = 1900
3x = 2400-1900,
3x = 500.
I understand the thing. But where the 3x goes?

Can somebody tell me?

78 is in kmph but answer is in meter so we should convert km to meter by 5/18 is the formula.

If you want to convert meter into km by 18/5.

Hi Thanu,

It's so simple ,Frist we convert km/hr in to m/sec becase train length is given in metres, so multiple speed with 5/18; Then it becomes into 78*5/18=65/3m/sec
Now we can find the length of tunnels say it as "x"metres.
use formula
speed=(length of tunnel+length of train)/60;where 1 minute=60 sec
x+800/60=65/3;After calculation x=500