Energy efficient lawn mower engine

An inventor has developed a new, energy efficient lawn mower engine. He claims that the engine will run continuously for 300 minutes on a single gallon of regular gasoline. From his stock of 2000 engines, the inventor selects a simple random sample of 50 engines for testing and finds the sample mean to be 295 minutes and sample standard deviation to be 20 minutes. Is there enough evidence to support his claim at the 5% level of significance? Assume the mean times are normally distributed. 1. A medical researcher says that less than 23% of US adults are smokers. In a random sample of 200 US adults, 19% say that they are smokers. At α = 0.05, is there enough evidence to support the researchers claim?