Quiz 2

Question 3

Only a single rail track exists between station A and B on a railway line. One hour after the north bound superfast train N leaves station A for station B, a south passenger train S reaches station A from station B. The speed of the superfast train is twice that of a normal express train E, while the speed of a passenger train S is half that of E. On a particular day N leaves for station B from station A, 20 minutes behind the normal schedule. In order to maintain the schedule both N and S increased their speed. If the superfast train doubles its speed, what should be the ratio (approximately) of the speed of passenger train to that of the superfast train so that passenger train S reaches exactly at the scheduled time at the station A on that day

1:5

16.36%

1:2

36.36%

1:3

31.82%

1:6

15.45%

initial ration is 1:4 because, E/2 divided by 2E we get, the same.
now, we know dist/speed=time.Form an eq. with this formula:-
so from the ratio 4x is the speed of superfast train and x is the speed of pass.train
D/4X (Time taken by superfast train) + D/X (Time taken by pass.train) = 60min
solving we get,
D/X =48, means that Time taken by pass.train is 48 mins.
12mins for superfast train.

For 20 mins later schedule,
superfast will double its speed, so it takes on 12/2 = 6mins.
Bal.14mins remains behind schedule.
48-14=34mins, means pass.train covering distance.
Final ratio=6:34 = 1:6 (round off 5.6)

Question 6

Inside the tunnel is a cat located at a point that is 3/8 of the distance AB measured from the entrance A. When the train whistles, the cat runs. If the cat moves to the entrance of the tunnel A, the train catches the cat exactly at the entrance. If the cat moves to the exit B, the train catches the cat exactly at the exit. The speed of the train is greater than the speed of the cat by what order ?

4:1

34.02%

1:2

25.77%

8:1

21.65%

None of these

18.56%

 

Let the speed of the train be St and the speed of the CAT be Sc.

Case 1:

The CAT runs towards the train.

Case 2:

The CAT runs away from the train.

Equating (i) and (ii),

St : Sc = 4 : 1  

Hence, option 1 is the correct one..

or

Let ‘c’ and ‘t’ be the velocity of train and cat.
Get the diagram right (if diagram is required)

1st case :
Train and cat meet at point A in the diagram.
Let train be at a distance of “y” from the entrance of the tunnel.
Cat is at a distance of 3x/8 from the entrance of the tunnel (Cat is between A&B. i.e. 3x/8 from A and 5x/8 from B )
So, by the time train runs a distance of y, cat runs a distance of 3x/8 (As they reach entrance at the same time)
Hence, equating the time taken, we have, y/t = 3x/8c

2nd case:
Train and cat meet at point B in the diagram.
Train travels a distance of y + x (Till the end of the tunnel)
Cat travels a distance of 5x/8 (Till the end of the tunnel)
Both reach at the same time, hence we can equate the time. We get, y + x/t = 5x/8c.

Subtracting the 2 equations, we have, (2nd case – 1st case) :
[(y +x)/t] – [y/t] = (5x/8c) – (3x/8c)
x/t = 2x/8c
c/t = 1/4.
t/c = 4/1.

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