A published study found that 75% of diesel cars in a large random sample registered in 2022 had CO emissions of less than 0.3 g/km.
Jo wants to investigate whether the proportion of diesel cars with CO emissions of less than 0.3 g/km has changed in the later year. She will carry out a hypothesis test at the 10% significance level, with a probability of at most 0.05 in each tail, using a random sample of 30 diesel cars registered in the later year.
State suitable null and alternative hypotheses for Jo's test.
Using a 10% significance level, find the critical region for Jo's test.
In her random sample, Jo finds 22 cars with CO emissions of less than 0.3 g/km. State Jo's conclusion in context.