1. + -133 points DevoreStat97,E.006 My Notes Ask Your Teacher On the basis of ex
ID: 3063728 • Letter: 1
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1. + -133 points DevoreStat97,E.006 My Notes Ask Your Teacher 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 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 (a) Assuming this to be the case, if a sample of 25 modified bars resulted in a sample average yield point of 8404 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 94967(Round your answer to two decimal places.) Select should be changed toExplanation / Answer
Ans:
Given that
standard deviation=100
sample size=25
standard error of mean=100/sqrt(25)=20
a)z value for 90% CI is 1.645
90% Confidence interval for mean
=8404+/-1.645*20
=8404+/-32.9
=(8371.1, 8436.9)
b)for 94% CI 1.881
94% CI for mean
=8404+/-1.881*20
=8404+/-37.62
=(8366.38, 8441.62)
it will be wider
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