Ask your teacher on the basis of extensive tests, the yield point of a particular type of mild steel-reinforcing bar is known to be normally distributed with σ = 100. the composition of the bar has been slightly modified, but the modification is not believed to have affected either the normality or the value of σ.

(a) assuming this to be the case, if a sample of 49 modified bars resulted in a sample average yield point of 8403 lb, compute a 90% ci for the true average yield point of the modified bar.
(b) how would you modify the interval in part (a) to obtain a confidence level of 96%? (round your answer to two decimal places.)