The lengths of steel rods, XXX cm, have a normal distribution with unknown mean μ\muμ cm and known standard deviation σ\sigmaσ cm. A random sample of 64 rods yielded a 95% confidence interval for μ\muμ of (12.18,12.62)(12.18, 12.62)(12.18,12.62).
Without carrying out any further calculations, use this confidence interval to test whether or not μ=12.7\mu = 12.7μ=12.7. State your hypotheses clearly and write down the significance level you have used.
A second random sample, of 80 rods, had a mean length of 12.4512.4512.45 cm.
Calculate a 99% confidence interval for μ\muμ based on this second sample.
