. A car drives 60 miles at an average speed of 30 miles per hour. How fast should the driver drive to travel the same 60 miles in the same time period, but at an average of 60 miles per hour?

This is not possible. To travel 60 miles at an average speed of 30 miles per hour, 2 hours are required; to travel at an average of 60 miles per hour in those same 2 hours, you’d need to go 120 miles rather than 60 miles.

The most common mistake is to respond with 90 miles per hour or 120 miles per hour – if you get a question like this in an interview, be sure to ask clarifying questions that could point you in the right direction.

In this case, for example, we might have reframed the question and asked if it was really, “How do you travel 60 miles in 2 hours at an average speed of 60 miles per hour?” If he said yes, we’d instantly know it was not possible.