We wish to see if, on average, traffic is moving at the posted speed limit of 100 km per hour along a certain stretch of an interstate highway. On each of four randomly selected days, a randomly selected car is timed and the speed of the car is recorded. The observed speeds are 105, 100, 105, and 110 km per hour.

Assuming that speeds are Normally distributed with mean μ, we test whether, on average, traffic is moving at 100 km per hour by testing the hypotheses