I understand average speed = total distance / total time.

But how exactly is 'total time' defined?

For example, in this kind of question, which solution would be the right one?

Q: A man spent 30 minutes driving from Town A to Town B. He then took a 15 minute break before driving from Town B back to Town A along the same route. If the distance between Town A and Town B is 60km, and he took 45 minutes on the return trip, what is his average speed?

In this case the total distance would be 60 + 60 = 120km

Total time = 30 + 15 + 45 = 90 OR 30 + 45 = 75?

It depends on the context and the way the question is defined. Either could be right. Usually, one would expect the problem to be defined such that you could tell what they are looking for.

In the problem the way you present it, I would include the 15 minutes as part of the total elapsed time. My reason for doing that would be that the 15 minute stop is relatively short and could be construed as being part of the trip in question (ie a round trip between A & B). If the problem specified average driving speed it would be simple, you would not include the 15 minutes. But, there is no universal definition of this, so it is hard to argue one way or the other. A certain amount of this in the classroom could depend on how the teacher presents other problems. It is poor problem definition to word a problem this way unless the classroom context shows how they would like it considered.

For a comparison, if the problem stated that the man stayed in Town B for 1 month before returning to Town A, you clearly would only consider the driving time. Some may maintain this as a reason to not include the 15 minute break in the first case.

So, my answer is that it is a poorly worded question that could be answered either way, with my preference to including the 15 minutes. Maybe some of our experts like Unknown and Perito who are a little closer to current classroom approaches than I can weigh in on this.

Thanks Zazonker! You made me blush... :o

Most of the time, the 'break' here is considered as 'catching point' or 'trap'. The time is mostly referred to the time during which traveling occurred. So I would not have included the 15 min break.

Thanks, Jerry.
Mathsolver, I recommend going with Unknown's answer.

Thank you so much Zazonker and Unknown008! Both of you have been informative and cleared my doubts.

You're most welcomed mathslover! If one really loves math, that one will try his/her best to understand everything he/she encounters in that subject, right? ;)