We love helping people think critically and solve problems—skills that are key to test success and beyond! This month’s brain teaser is a classic. Enjoy!
If a car drives the 60 miles from San Jose to San Francisco at an average speed of 30mph, at what average speed must the car make the return trip to achieve an average speed for the entire trip of 60mph?
Answer:
It seems counterintuitive at first, but it’s impossible. In order to have an average speed of 60mph for the entire trip, the car must travel for 2 hours (if the car travels a total distance of 120 miles, then its total time must be 2 hours: 120miles/2 hours = 60 miles per hour). But if the car traveled at an average speed of 30mph for the first 60 miles then it already spent 2 hours. So it is impossible to achieve an average speed of 60mph!