Supposethatamarketresearchfirmishiredtoestimatetheproportionofpeoplelivinginalargecityin Victoria who have cell phones. Of the 500 people surveyed, 421 responded yes - they own cell phones.

(a)Using a 95% confidence level, compute a confidence interval estimate for the population proportion

of people of this city who have cell phones. Show your working and give your answer to three decimal places Interpret the confidence interval.

Supposetheresearcherwants totest whethertheproportion of allpeoplewho havecell phonesis

different from 85%.

(i)Write the null and alternative hypotheses for this test.

(ii)Define the term "Type I error".

What is a Type I error in the context of the hypothesis test in part (b)(i)?