As a result of the massive shift from full-service to self-service gas stations, a consume...

As a result of the massive shift from full-service to self-service gas stations, a consumer’s group is concerned that many cars are being driven on underinflated tires. This results in excessive tire wear, and unsafe steering and braking of the car. A tire is considered to be seriously underinflated if its tire pressure is more than 10 psi under its recommended level. A random sample of 400 cars is selected and the mean underinflation is  psi, with a standard deviation of s = 4.2 psi.