How many seconds should elapse between two consecutive mile markers if the cars average speed is 65 miles per hour?

Assuming this is not a trick question, it can be restated:

If an automobile is traveling at 65 miles per hour, what is the interval in seconds to travel one mile?

There are a few approaches to solve this problem. The clearest one involves conversions between miles per hour and miles per minute etc. This kind of problem is sometimes used in an aptitude test, and knowing and understanding a shortcut method to get to the answer can be key to completing all of the problem on the exam.

In this case here is what I would do.

Background known fact is that 60 miles per hour is One Mile per minute-- one mile per 60 seconds. Quick thought on concept brings understanding that if you go FASTER than 60 mph, the time must be shorter than 60 seconds. In fact--- it is all linear and you can use a simple proportion. 60 mph divided by 65 mph times 60 seconds---- the answer is: 55.4 seconds to the nearest tenth.

A trick part to the question is that without first THINKING about the concept, and understanding that the answer MUST be less than 60 seconds, the temptation in running through an exam COULD be to remember the 60 seconds 60 mph relationship, and then quickly check off on multiple choice 65 seconds as the answer matching 65 MPH. Unfortunately that would be, of course, incorrect and the answer to the question would indicate in the test a flawed thinking process when stressed, or at least missing the concept of inverse relationships.