Question

3. The compressive strength of concrete when mixed with fly ash was investigated. Nine samples interval on the mean compressive strength in dry conditions were tested and a 90% confidence oo was found as [19.9,30.34).If the manufacturer claims that the mean compressive strength is 25 MPa, is the claim valid? (a) Yes (b) No (c) Not enough information nclusinnsegarding the totofthe hypotheses

please solve number 3. show work if possible.

Answer 1

For 90 % confidence Interval z = 1.645 Given confidence Interval [19.9, 30.34] The confidence Interval [x_1, x_2] is given as (x_1, x_2) = (mu - z sigma, mu + z sigma) Therefore mu - 1.645 sigma = 19.9 ...(1) mu + 1.645 sigma = 30.34 ..(2) Adding (1) & (2) , 2 mu = 50.24 or mu = 25.12 MPa thus, claim for mean (mu) = 25 MPa is correct and valid