Twenty-five wooden beams were ordered or a construction project. The sample mean and he sample standard deviation were measured xbar = 190cm, s = 5cm. Calculated confidence interval for the mean is [188.29; 191.71]. Which confidence level was chosen? Assume distribution to be normal.
A. 99%
B. 90%
C. 95%
D. 99.9%

Correct option: B. 90%

Explanation:

The confidence interval is given by:

If is 190, we can find the value of :

Now we need to find the value of :

So the value of z is 1.71.

Looking at the z-table, the z value that gives a z-score of 1.71 is 0.0436

This value will occur in both sides of the normal curve, so the confidence level is:

The nearest CI in the options is 90%, so the correct option is B.

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