The yield point of a particular type of mild steel-reinforcing bar is known to be normally distributed with s.d = 100. a) If n=25, and results in a sample average yield point of 8439 lb, compute a 95%...

The yield point of a particular type of mild steel-reinforcing bar is known to be normally distributed with s.d = 100.

a) If n=25, and results in a sample average yield point of 8439 lb, compute a 95% confidence interval for the true average yield point of the bar.

b) Is there compelling evidence for concluding that the true average amount of yield point of the bar differs from 8420. Use (alpha) = 0.05

c) What will be the sample size n if the width of the confidence intervcal in part a) is to be halved?