An article gave the following summary information for fracture strengths (mpa) of n = 169 ceramic bars fired in a particular kiln: x = 34.30, s = 3.92. calculate a (two-sided) confidence interval for true average fracture strength using a confidence level of 95%. (round your answers to two decimal places.) ) mpa 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 4 mpa. based on this supposition, how large a sample would have been required to estimate to within 0.5 mpa with 95% confidence? ceramic bars you may need to use the appropriate table in the appendix of tables to answer this question.