Exercise 15 of Section 12.2 included Minitab output for a regression of flexural strength of concrete beams on modulus of elasticity.

s 5 5.240 R-sq 5 97.5% R-sq(adj) 5 97.3%

21.128 20.48 runoff 5 21.13 1 0.827 y 5 runoff volume (both in m3

)

x 5 rainfall volume sbˆ 1 gy2 i 5 66,224, gxi yi 5 703,192 gxi 5 10,576, gyi 5 894, gxi 2 5 8,741,264, x 5 yield strength (MPa)

y 5 threshold stress (% SMYS)

a. Use the output to calculate a confidence interval with a confidence level of 95% for the slope b1 of the population regression line, and interpret the resulting interval.

b. Suppose it had previously been believed that when modulus of elasticity increased by 1 GPa, the associated true average change in flexural strength would be at most .1 MPa. Does the sample data contradict this belief?
State and test the relevant hypotheses.