Without stoppage, a train travels a certain distance with an average

Where am I wrong here?

Assume 100 miles covered

scenario 1 takes 2 hours
scenario 2 takes 2.5 hours

-> 0.5 hours of total stoppage, 2 hours of travel time

--> 0.5 hours / 2 = 15 minutes.

But OA is D. Where is my mistake?

Without getting too deeply into the underlying logic (it took me a bit to understand on my own ———>GMATinsight and CrackVerbal both have great explanations)


This is the kind of problem where you need to step back and think about what’s going on. What’s implied by the question is that the train’s actual speed when it’s driving never really changes.

The difference in the speed comes from making stops. I believe your calculation is working under the assumption that the train never stopped in the second case and was traveling at 40 kmph the whole 200 miles.


Here is how I was finally able to conceptualize it:

First, the question is asking for minutes of stoppage on a per hour basis, so we’ll calculate every on a per hour basis.


Case 1: the train does not stop at all and drives for the entire 1 hour or 60 min

Over 60 min not stopping ————> the train can cover 50 km

Which means, as CrackVerbal showed above (when it’s broken down on a per 1 km basis)

Every 6/5 minute that passes when the train does not stop and travels continuously ———-> the train covers 1 km

Case 2: the key to understanding the difference here is to note that the train’s speed WHILE DRIVING has not changed

The average speed’s definition is literally how much distance can be covered in a set time

The stops make it so the train can now only cover 40 km every 60 min

Thus with the stops:

Every 60 minutes that passes ————> the train is only able to cover 40 km

We found above that WHILE DRIVING the train can cover 1 km ———-> every 6/5 minutes

If the train actually covered 40 km ———-> then the train must have been driving for (40) (6/5) = 48 minute out of the 1 hour

The other 12 minutes must have been spent stopped.


Each hour 12 min are spent stopping.

It’s tricky, if you spend some time thinking about it you’ll eventually get it (took me a bit)




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Hey MV94, I made the same mistake as you did. The highlighted portion is where you (and I) went wrong. The total travel time is 2.5 hours for the second scenario and that is what we need to consider. 30 minutes of stoppage time happened in the 2nd scenario, so you need to divide 30 minutes by 2.5 hours, which gives you 12.

distance covered in 1 hour without stoppage ; 50 km
with stoppage 50 km will be covered in 50/40 ; 5/4 hrs
difference of time will give stoppage duration ; 5/4- 1 ; 1/4 hrs which is stoppage duration
target of question is how many minutes per hour does the train stop during the journey
we know that total hours of journey is 5/4 hours so in min/hours the stoppage will be

1/4 *60 *4/5 = 12 mins/hr
option D

A -> 50kph
B -> 40kph
D=s*t

tA = 20/50 * 60 = 24 min
tB = 20/40 * 60 = 30 min

lag time = 30 min - 24 min = 6 min

if in half an hour there was a 6 min stop, if the trend is maintained then it means that in an hour we'll have 6*2 = 12 min of stoppage.

­The speed reduces from 50 km/hr to 40 km/hr i.e. 20%. so the stoppage time would be 20% of60 mins i.e. 12 min per hour

Time = Distance (D)/Speed
Time taken without stoppage = D/50 hrs
Time taken with stoppage = D/40 hrs
Total extra time taken due to stoppage = D/40 - D/50 = D/200 hrs
Rest time per hour = D/200 / D/40 = D/200 x 40/D = 1/5 hrs = 12 min