The value of z* should be used to construct a 97 confidence interval of a population mean is 2.17.
<h3>What is confidence interval?</h3>
A degree of uncertainty and certainty in a sample process is measured by confidence intervals. They can choose from a variety of probability limitations, the most frequent becoming a 95% or 99% confidence level.
Some characteristics of confidence interval are-
- Statistical tools, such as the t-test, are used to compute confidence intervals.
- Confidence intervals are used by statisticians to quantify uncertainty in such a sample variable.
- A researcher, for example, may randomly select multiple samples drawn from the same population and compute a confidence interval for every sample to determine how well it might represent the real value of a population variable.
- The generated datasets are all unique; some intervals contain the genuine population parameter while others do not.
Now, according to the question;
The confidence level is given 97%.
Thus, the crucial value of z for a 97% confidence interval is 2.17, as determined by a z score table, which is as follows:

Therefore the obtained probability for the z-score of 2.17 is 0.97.
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Answer:
25.9%
Step-by-step explanation:
100000÷13500×100
Subtract the 74.074 because 100000 is 74.074 of 135000
Let x be the required waranty period, then
P(X < x) = P(z < (x - 12)/(8/12)) = 1 - 0.067 = 0.933
P(z < 12(x - 12)/8) = P(z < 1.498)
12(x - 12)/8 = 1.498
x - 12 = 8(1.498) / 12 = 0.9987
x = 12 - 0.9987 = 11
Therefore, they should waranty for 11 years so that no more than 6.7% fail within that time.
cost of production = %13
Let the price be p, then
revenue less price of failed iron = p - 0.067(13) = p - 0.871
Profit = p - 0.871 - 13 = 5
p - 13.871 = 5
p = 5 + 13.871 = 18.871
Therefore, the should charge $18.87 per waffle iron.
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