Can someone help to answer this type of question:

That's how I would approach this problem:

1. #trains = #line multiply by #train per line

2. #train per line= frequency of train (how long I wait at a given station) multiply by average time between two station

Assumptions:

- Let's say that during peak hours I have to wait maximum 3 minutes at a given station to have a train and that the length of time between two station is 1min30

- there is 14 lines in Paris and on average 21 stations per line

________

if I must wait 3 minutes to get a train it means that there is one train every three stations at a given time (so 21/3= 7 trains per line)

As there is two ways in a line we must double it to 14 trains per line

Finally there is 14 lines so we must multiply 14 by 14 which gives me 196 trains

By doing some research I found out that this number is relatively low (approximately 500 trains during peak hours)

How would you approach this problem?

Thanks for your help

Can you explain why you did 55/(3+1). I don't understand the rationale behind 3+1. Thanks in advance