Question

An article gave the following summary information for fracture strengths (MPa) of n = 144 ceramic bars fired in a particular kiln: x = 44.95, s = 3.38.
(a) Calculate a (two-sided) confidence interval for true average fracture strength using a confidence level of 95%. (Round your answers to two decimal places.)

Does it appear that true average fracture strength has been precisely estimated?

Yes, this is a very narrow interval.
No, this is a very wide interval.

(b) Suppose the investigators had believed a priori that the population standard deviation was about 7 MPa. Based on this

Answer 1

I got the first part and I think the interval is narrow.

Answer 2

@freckles

Answer 3

@IrishBoy123