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Confidence Interval Part 2

# Confidence Interval Part 2 - interval for the true...

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2/26/2008 1 Confidence Intervals & Sample Size, Part 2 Conclusion of Chapter 7 Example 2 . Estimate with 98% confidence the mean gallons of water needed to wash the cab of a Kenworth 18-wheeler truck. The population of gallons needed to wash cabs is assumed to be normal. For a sample of 16 washes the mean was 32.00 gallons and the standard deviation was 6.4 gallons. Whichdistribution should we use (z or t)? Example, cont’d.

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2/26/2008 2 Example, cont’d.
2/26/2008 3 Example (pg. 381 #2) Presidential Travel: In a survey of 1004 individuals, 442 felt that President George W. Bush spent too much time away from Washington. Find a 95% confidence

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Unformatted text preview: interval for the true population proportion. What do we know? Example, cont’d. You try one…. •You try #4 page 370. 2/26/2008 4 Sample size for proportions • Car Phone Ownership: A researcher wishes to estimate the proportion of people who own a home computer. A previous study shows that 40% of those interviewed had a computer at home. The researcher wishes to be accurate within 2% of the true proportion. She wants also to be 90% confident. Find the minimum sample size necessary. Example, cont’d. • What do we know? You try one… • You try one: – Try #12 page 382. 2/26/2008 5...
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Confidence Interval Part 2 - interval for the true...

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