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Did You Find Out? Get the Answer to the Riddle of E-News Issue No. 03, July 2013

How fast does he need to drive?
How fast does he need to drive?

A race driver is testing a new engine in a race car. The technicians give him the following instructions:

  • "Drive two laps around the race track in total."
  • "In the first lap, warm up the engine. To do this, maintain an average speed of 40 km/h (25 mph)."
  • "In the second lap, drive fast enough to achieve an average speed of 80 km/h (50 mph) over the total two laps."

Question: What is his top speed for the second lap?

Answer

The distance can be ignored. In this example, a lap distance of 40 km (25 miles) is presumed.

  • Driving an average speed of 80 km/h (50 mph) for two laps (80 km, 50 miles) a total time of 1 hour is needed.
  • The driver has to drive 40 km/h (25 mph) for the first lap. Here, he will already need one hour.
  • Thus, he would need to complete the second lap in 0 seconds, which means that he would need to drive at an infinite speed!

The conclusion is that the race driver cannot fulfill the requirements. He would need to drive at an infinite speed in the second lap to reach an average speed of 80 km/h (50 mph) over the total two laps.