Apple is one of the most popular companies in the world. Data shows Apple's iPhone took up to 48.8% of all cell phones sold in the U.S. last year(2020).

a). Suppose a group of students researched the percentage of their classmate who uses an iPhone. Their result showed that 287 of 400 students in their school use iPhones. Find the smallest significance level so that the market data's report is reasonable?

b). Suppose those students want to update data for this year (2021). They reached out to the 1300 residents in their community and found n number of people uses iPhone. What value of n would lead to a hypothesis test which rejects the null hypothesis (alpha = 0.05)? (graph or calculator allowed)

c). The students found that the iPhones are much more prevalent among upper grades. So they did a separate test for each grade (freshman, sophomore, junior, and senior). They found that those groups made up 35%, 27%, 19%, and 11% of iPhone users, respectively. Suppose they gathered the data from the other high school in the community (39 freshmen, 76 sophomores, 150 junior, and 176 senior iPhone users). Conduct a hypothesis test with a significant level of 0.02 to see if their percentage result is reasonable.