Question

A civil engineer wishes to see if the tensile strength of the steel will change if it is exposed to extreme temperature. Six rebars were pretested, and then they were exposed to the extreme heat 6-week period. The results are shown in the table. Can it be concluded that tensile strength has been change at α=0.10. Assume the variable is approximately normally distributed. Determine also the confidence interval at 90%.

8. A civil engineer wishes to see if the tensile strength of the steel will change if it is exposed to extreme temperature. Six rebars were pretested, and then they were exposed to the extreme heat 6-week period The results are shown in the table. Can it be concluded that tensile strength has been changed at a 0.10? Assume the variable is approximately normally distributed. Determine also the confidence interval at 90% Subject Before (x.) 210 235 208 190 172 244 After (X) 190 170 210 88 173 228

Answer 1

8)

from above as test statistic is not in critical region we cannot reject null hypothesis

we do not have sufficient evidence to conclude that tensile strength has changed as 0.10 level of significance,

b)

for 90% CI; and 5 degree of freedom, value of t=			2.015
therefore confidence interval=		sample mean -/+ t*std error
margin of errror          =t*std error=		20.887
lower confidence limit                     =		-4.220
upper confidence limit                    =		37.553