A sample of 30 is taken from a population of Inconel weldments. The average thickness is 1.87 inches at a key location on the part. The sample standard deviation is 0.125 inches and will be used as an estimate of population standard deviation. Calculate the 99% confidence interval. (Hint: Z(a/2) is 2.58 for a 99% CI)a. (1.811, 1.929)b. (1.611, 1.729)c. (1.711, 1.829)d. (1.511, 1.629)

a. (1.811, 1.929)

Step-by-step explanation:

We have to find find M as such

In which, z is Z(a/2), is the standard deviation of the population and n is the size of the sample. So

The lower end of the interval is the mean subtracted by M. So it is 1.87 - 0.059 = 1.811.

The upper end of the interval is the mean added to M. So it is 1.87 + 0.059 = 1.929

So the correct answer is:

a. (1.811, 1.929)

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step-by-step explanation:

du what else would it be

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