Question

There is only one rail track between stations A and B on a railway line. One hour after the northbound superfast train N leaves station A for station B, the southbound passenger train S reaches station A from station B. The speed of superfast train is twice that of express train E, while the speed of passenger train S is half of that of train E. On some one day train N leaves from station A to station B 20 minutes late than its usual schedule. Both Train N and Train S have increased their speed to maintain the schedule as per the table. If the superfast train doubles its speed, then what should be the ratio (approximately) of the speed of the passenger train to the speed of the superfast train so that the passenger train reaches the station on that day at the exact scheduled time.
1. 1 ∶ 4
2. 1 ∶ 5
3. 6 : 1
4. 3 : 17

Answer 1

Correct Answer - Option 4 : 3 : 17

Given: 

Ratio of the speeds of train N, E and S = 4 : 2 : 1

Formula used:

Speed = Distance/Time

Assumptions:

Let the time taken by N and S to reach the destination points B and A  is 12 minutes and 48 minutes respectively.

We assume the total distance from A to B be 48 m 

The speed of N and S be 4 m/minute and 1 m/minute 

Let the starting time be 9am 

Calculation:

New speed of N = 8 m/minute 

Time taken from A to B = 48/8 = 6 minutes 

N leaves at 9:20 am and reaches at B at 9:26 am 

So, new speed of S = 48/34 = 24/17 m/minute

Ratio of speed of S and N = 24/17 : 8 

⇒ 3 : 17 

⇒ 3  : 17 

Note∶ The question options was incorrect in the official paper. However, we have changed it and update it accordingly.