Answer :
Complete Question
A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with[tex]\sigma^2=1000[/tex]. A random sample of 12 sample specimens has a mean compressive strength of [tex]\=x=3207psi[/tex]. Round your answers to 1 decimal place. (a) Calculate the 95% two-sided confidence interval on the true mean compressive strength of concrete.
Answer:
[tex]CI=(3189.1,3224.9)[/tex]
Step-by-step explanation:
From the question we are told that:
Sample size [tex]n=12[/tex]
Standard deviation [tex]\sigma^2=1000psi^2\\\sigma=\sqrt{1000} \\\sigma=31.6[/tex]
Sample mean [tex]\=x=3207[/tex]
Confidence level =95%
[tex]\alpha=100-95\\\alpha=0.05[/tex] significance level
From table \alpha 0.05
Gives
[tex]Z_c=1.96[/tex]
Generally the equation for confidence interval is mathematically given by
[tex]CI=(\=x-\frac{z_c*\sigma}{\sqrt{n} } ),\=X+\frac{Z_C*\sigma}{\sqrt{12} })[/tex]
[tex]CI=(3207-\frac{1.96*31.6}{\sqrt{12} } ),3207+\frac{1.96*31.6}{\sqrt{12} })[/tex]
[tex]CI=(3189.1,3224.9)[/tex]