Solution to: Speedy Sums
At 120 km/h, it took the racecar driver 1 minute to cover the first 2 km. To reach an average speed of 240 km/h for 4 km, that distance must be travelled in 1 minute. However, that time was already used up in the first half of the course. Therefore, the answer is that, no matter how fast the racecar drives in the second part of the course, it is impossible to average 240 km/h for the entire course!