A salesman drives from Amsterdam to The Hague. The first half of the distance of his journey, he drives at a constant speed of 80 km/h. The second half of the distance of his journey, he drives at a constant speed of 120 km/h.

The question: What is the salesman's average speed for the complete journey?

A hint : The solution is not 100 km/h!

The answer: Click here!

Another question: A racecar driver drove, on a 4 km long racecourse, at an average speed of 120 km/h for the first 2 km. How fast does he have to go the second 2 km to average 240 km/h for the entire course?

Another answer: Click here!

Yet another question: Makkum and Stavoren are two villages. Michael and Donald want to go from Makkum to Stavoren. They leave at the same time. Michael goes by bicycle. Donald goes by car, which is six times as fast as Michael is on his bicycle. Unfortunately, Donald has a car breakdown halfway between Makkum and Stavoren. Fortunately, a passing farmer gives him a lift to Stavoren on his tractor. Unfortunately, the farmer drives only half as fast as Michael drives on his bicycle. Who of the two arrives first in Stavoren?

Yet another answer: Click here!

The fourth question: Normally, the train between Utrecht and Amersfoort drives at an average speed of 90 km/h. One day, the train was delayed a little. Because of this, the average speed of the train between Utrecht and Amersfoort was only 70 km/h, and the train arrived four minutes late in Amersfoort. What is the distance between the stations of Utrecht and Amersfoort?

The fourth answer: Click here!