Chapter 7: Inferences Based on a Single Sample: Estimation with Confidence Intervals
Quiz 2



1.  

A 90% confidence interval for the mean percentage of airline reservations being canceled on the day of the flight is (4.8%, 11.2%). What is the point estimator of the mean percentage of reservations that are canceled on the day of the flight?



2.  

You are interested in purchasing a new car. One of the many points you wish to consider is the resale value of the car after 5 years of ownership. Since you are particularly interested in Toyota Camry, you decide to estimate the resale value of the Camry with a 90% confidence interval. You manage to obtain data on 17 recently resold 5 year old Toyota Camrys. These 17 cars were resold at an average price of $12,400 with a standard deviation of $700. What is the correct form of a 90% confidence interval for the true mean resale value of a 5 year old Toyota Camry?



3.  

How much money does the average professional football fan spend on food at a single football game? That question was posed to ten randomly selected football fans. The sampled results show that sample mean and standard deviation were $52.00 and $17.50, respectively. Use this information to determine the true mean food sales for a 95% confidence interval.



4.  

It is desired to estimate the average total compensation of CEOs in the Service industry. Data were randomly collected from 18 CEOs and the 97% confidence interval was calculated to be ($2,181,260, $5,836,180). What assumptions are necessary for this confidence interval to be valid?



5.  

A confidence interval was used to estimate the proportion of statistics students that are females. A random sample of 72 statistics students generated the following 90% confidence interval: (.438, .642). State the level of reliability used to create the confidence interval.



6.  

In the construction of confidence intervals, if all other quantities are unchanged, an increase in the sample size will lead to a __________ interval.



7.  

A statistician in a mail order house wished to estimate how many mail order parcels prepared last Friday by the wrapping and packaging department were improperly packaged. He took a random sample of 2 percent of all the parcels prepared that day, had the sample parcels unwrapped and inspected, and found that 20 were improperly packaged. He reported that 1,000 mail order parcels were improperly packaged on Friday. The statistician's report utilized:



8.  

A computer package was used to generate the following printout for estimating the sale price of homes in a particular neighborhood.

X = sale_price

SAMPLE MEAN OF X = 46300
SAMPLE STANDARD DEV. = 13747
SAMPLE SIZE OF X = 25
CONFIDENCE = 90

UPPER LIMIT = 51003.9
SAMPLE MEAN OF X = 46300
LOWER LIMIT = 41596.1

What assumptions are necessary for any inferences derived from this printout to be valid?



9.  

What type of car is more popular among college students American or Foreign? One hundred fifty-nine college students were randomly sampled and asked which type of car they drove. A computer package was used to generate the printout below for the proportion of college students who drive American automobiles.

SAMPLE PROPORTION = 0.396226
SAMPLE SIZE = 159

UPPER LIMIT = 0.46424
LOWER LIMIT = 0.331153

What proportion of the sampled students drive foreign automobiles?



10.  

To help consumers assess the risks they are taking, the Food and Drug Administration (FDA) publishes the amount of nicotine found in all commercial brands of cigarettes. A new cigarette has recently been marketed. The FDA tests on this cigarette gave a mean nicotine content of 26.4 milligrams and standard deviation of 2.0 milligrams for a sample of n = 9 cigarettes. Construct a 90% confidence interval for the mean nicotine content of this brand of cigarette.

Note: answer choices in this exercise are randomized.

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