Aptitude - Problems on Trains - Discussion

Nice explanation @Gaurav Reddy.

Thanks @Randhir.

Thanks @Nagarjun.

Thank you @Randhir.

Please any one explain why we divide 176/8?

@Priya,

Speed=Distance/Time.
here Distance=length of train + length of bridge.

in this question we have no idea about the length of train and speed of the train.
so let the length of the train be x metres and speed be y m/sec.
then speed of train y = (x+264)/20.

we can't solve because vale of x and y is unknown.
now speed of the train relative to telegraph post
i.e. y = x/8.
comparing the two above equation
x/8 = (x+264)/20
3x = 528
x = 176 which is length of train.
now put the value of x in any of the above two equation.
therefor speed y = 176/8
y = 176/8 *18/5 (because to convert in kmph)
y = 79.2 km/hr

S = x/8 m/s.
S = d/t.
x/8 = (264+x)/20.

Solve it and you will get:

x = 176 m.
S = 176/8 = 22 m/s.

Now convert m/s to km/hr.
22*(18/5) = 79.2 km/hr.

That's it.

Hey can anyone tell me instead of taking x/y=8 , Can we take x/y=20 because it is also time ?

In question No. 19 x/y=15 is mentioned as x/15=y. But in this question when x/y=8 is mentiond as x=8y. What is the reason for this? please explain me.

Why we didn't add time. While calculating the speed. We taken only 20. Why we didn't take 20+8?