Question 1 (1 mark) Attempt 1 On the basis of extensive tests, the yield point o

Question

Question 1 (1 mark) Attempt 1 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 a standard deviation of 450 Nt. The composition of the bar has been slightly modified, but the modification is not believed to have affected the normality or the standard deviation. Assuming this to be the case, if a sample of 38 modified bars resulted in a sample average yield point of 34240 Nt, construct a 99% confidence interval for the true average yield point of the modified bar Za a(tail area) 0.1 0.05 0.025 0.01 0.005 0.001 %ile 90 95 97.5 99 99.5 99.9 1.282 1.645 1.960 2.326 2.576 3.090 Your answers can be rounded to one decimal digit accuracy when entered Lower limit isSkipped Upper limit isSkipped

Explanation / Answer

Solution:- Given that x = 34240, sd = 450, n = 38 99% confidence interval = 2.326

=> 99% confidence interval : X +/- Z*s/sqrt(n)

: 34240 +/- 2.326*450/sqrt(38)

: 34070.2 , 34409.8

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