4.2A bank manager wants to estimate the mean time a teller spends with a business customer. If the time is assumed to be normally distributed and the population standard deviation is believed to be 6 minutes, how large a sample should be taken so that the error is less than 2 minutes with 95% confidence?

4.3Leading up to each Federal Election, the various opinion pollsters conduct nationwide surveys of electors in an attempt to forecast the proportion of the electorate who will vote for each of the major parties. Suppose that a polling firm conducts a survey of 500 randomly selected electors (a representative sample), and their results indicate that 210 of these electors will vote for the ALP at the election. Construct a 95% Confidence Interval for the (true) proportion of voters who will vote for the ALP at the election.