Under her cell phone plan, Ellie pays a flat cost of $50 per month and $5 per
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Using the z-distribution, it is found that the 90% confidence interval is given by: (0.6350, 0.6984).
<h3>What is a confidence interval of proportions?</h3>A confidence interval of proportions is given by:
In which:
is the sample proportion.
- z is the critical value.
- n is the sample size.
In this problem, we have a 90% confidence level, hence, z is the value of Z that has a p-value of
, so the critical value is z = 1.645.
The sample size and the estimate are given by:
Hence, the bounds of the interval are given by:
The 90% confidence interval is given by: (0.6350, 0.6984).
More can be learned about the z-distribution at brainly.com/question/25890103
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