A vehicle completes a fixed route in 2.5 hours at a constant speed of 72 kilometres per hour. How long would the same route take at 90 kilometres per hour?

Explanation

The route is 72 times 2.5, or 180 kilometres, so at 90 kilometres per hour it takes 180 divided by 90, which is 2 hours. A time of 3.125 hours comes from increasing time with speed as if they were directly proportional, contrary to a fixed distance.