# Confidence Interval Examples

This is a collection of a handful of statistics problems that ask for Confidence intervals. Specifically, this is broken up 3 ways: Confidence interval for mean (sigma known), Confidence interval for mean (sigma unknown), and proportion.

There are many many questions in the document attached. For example

Example 1:
The average life of light bulbs produced by SABA Electric Co. is believed to be normally distributed with the mean service life of 950 hours and a standard deviation of 100 hours. A random sample of 100 bulbs is tested and it has a mean life of 930 hours. Calculate the 99% confidence interval for mean lightbulb life

Example 2:
Safe Lumber Company hires an independent contractor to monitor the groundwater within a one mile radius of its factory to ensure that no toxic levels of arsenic are being released. The contractor takes a sample of groundwater from selected sites within the one mile radius. Suppose that data from 25 sites had arsenic levels averaging 75 ppb with a sample standard deviation of 30 ppb. Construct a 95% confidence interval for the arsenic level.

Example 3:
Borrowers Bank classifies credit cardholders as “prime” whenever they pay interest charges for at least 6 of the last 12 billing cycles. The table below cross classifies 2080 cardholders according to whether they are 1) prime or not, and 2) below age 30 or not

Solutions to prior projects are given all dealing with confidence intervals. The first problem is provided with full solution.

Subjects: Statistics
Topic: Homework problems for Confidence Intervals (Statistics)
Level: College / University
Tags:

### statistics, analysis, confidence interval, alpha

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Project Details
Subjects: Statistics
Topic: Homework problems for Confidence Intervals (Statistics)
Level: College / University
Tags:

## statistics, analysis, confidence interval, alpha

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