A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with oʻ = 1000 (psi)? .A random sample of 12 specimens has a mean compressive strength = 3250 psi. a) Construct a 95% two-sided confidence interval on mean compressive strength. b) Construct a 99% two-sided confidence interval on mean compressive strength. Compare the width of this confidence interval with the width of the one found in (a). c) Suppose that it is desired to estimate the compressive strength with an error that is less than 15 psi at 99% confidence. What sample size is required?

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Please can you solve this question about confidence interval of mean of normal distribution. From probability and statistics for engineering course.

A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with oʻ =
1000 (psi)? .A random sample of 12 specimens has a mean compressive strength = 3250 psi.
a) Construct a 95% two-sided confidence interval on mean compressive strength.
b) Construct a 99% two-sided confidence interval on mean compressive strength. Compare the
width of this confidence interval with the width of the one found in (a).
c) Suppose that it is desired to estimate the compressive strength with an error that is less than
15 psi at 99% confidence. What sample size is required?
Transcribed Image Text:A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with oʻ = 1000 (psi)? .A random sample of 12 specimens has a mean compressive strength = 3250 psi. a) Construct a 95% two-sided confidence interval on mean compressive strength. b) Construct a 99% two-sided confidence interval on mean compressive strength. Compare the width of this confidence interval with the width of the one found in (a). c) Suppose that it is desired to estimate the compressive strength with an error that is less than 15 psi at 99% confidence. What sample size is required?
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