Question

On the basis of extensive tests, the yield point of a particular type of mild steel-reinforcing bar is known to be normally distributed with σ = 100. The composition of the bar has been slightly modified, but the modification is not believed to have affected either the normality or the value of σ.

(a) Assuming this to be the case, if a sample of 49 modified bars resulted in a sample average yield point of 8429 lb, compute a 90% CI for the true average yield point of the modified bar. (Round your answers to one decimal place.)

  ,

lb

(b) How would you modify the interval in part (a) to obtain a confidence level of 98%? (Round your answer to two decimal places.)

---Select--- The value of z The sample size The standard deviation The sample mean should be changed to  .

Answer 1

From the given information,

By using calculator,

The required correct answers are,

a. The 90% confidence interval is given by,

( 8405.5 lb , 8452.5 lb )

b. The value of z should be changed to 2.33

Thank you.

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