5 A builders' merchant sells stones of different sizes.
- The masses of size \(A\) stones have standard deviation 6 grams. The mean mass of a random sample of 200 size \(A\) stones is 45 grams.
Find a 95\% confidence interval for the population mean mass of size \(A\) stones.
- The masses of size \(B\) stones have standard deviation 11 grams. Using a random sample of size 200, an \(\alpha \%\) confidence interval for the population mean mass is found to have width 4 grams.
Find \(\alpha\).