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Chapter 8: Q.48 (page 480)
Why would the error bound change if the confidence level were lowered to?
The error bound will become smaller if the confidence level were lowered to,
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Table shows a different random sampling of cell phone models. Use this data to calculate a % confidence interval for the true mean SAR for cellphones certified for use in the United States. As previously, assume that the population standard deviation is 蟽= .
| Phone Model | SAR | Phone Model | SAR |
| Blackberry pearl | Nokia E71x | ||
| HTC Evo Design 4G | Nokia N | ||
| HTC Freestyle | Nokia N | ||
| LG Ally | Sagem Puma | ||
| LG Fathom | Samsung Fascinate | ||
| LG Optimus Vu | Samsung Infuse 4G | ||
| Motorola Cliq XT | Samsung Nexus S | ||
| Motorola Droid pro | Samsung Replenish | ||
| Motorola Droid Razr M | Sony W5a walkman | ||
| Nokia Twist | ZTE C |
Unoccupied seats on flights cause airlines to lose revenue. Suppose a large airline wants to estimate its mean number of unoccupied seats per flight over the past year. To accomplish this, the records of 225 flights are randomly selected and the number of unoccupied seats is noted for each of the sampled flights. The sample mean is 11.6 seats and the sample standard deviation is 4.1 seats.
a. i. __________
ii. __________
iii. __________
iv. __________
b. Define the random variables and in words.
c. Which distribution should you use for this problem? Explain your choice.
d. Construct a 92% confidence interval for the population mean number of unoccupied seats per flight.
i. State the confidence interval.
ii. Sketch the graph.
iii. Calculate the error bound.
Suppose that a committee is studying whether or not there is waste of time in our judicial system. It is interested in
the mean amount of time individuals waste at the courthouse waiting to be called for jury duty. The committee randomly
surveyed people who recently served as jurors. The sample mean wait time was eight hours with a sample standard
deviation of four hours.
b. Define the random variables in words.
c. Which distribution should you use for this problem? Explain your choice.
d. Construct a confidence interval for the population mean time wasted.
i. State the confidence interval.
ii. Sketch the graph.
iii. Calculate the error bound.
e. Explain in a complete sentence what the confidence interval means.
You do a study of hypnotherapy to determine how effective it is in increasing the number of hours of sleep subjects get each night. You measure hours of sleep for subjects with the following results. Construct a % confidence interval for the mean number of hours slept for the population (assumed normal) from which you took the data. ; ; ; ; ; ; ; ; ; ; ;
A poll of 1,200 voters asked what the most significant issue was in the upcoming election. Sixty-five percent answered the economy. We are interested in the population proportion of voters who feel the economy is the most important.
Define the random variable P鈥� in words.
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