CI for a Population Mean
Find the critical values, tc, given n=25 using a 99% level of confidence.
What is +/- 2.797.
Given that 90 out of 200 adults were smokers, find the point estimate for the population proportion of adults who are smokers. Be sure to attach a symbol to it.
What is p-hat = 0.45
What distribution must be used when computing confidence intervals for variances and standard deviations?
What is Chi-square
A confidence interval is an _____________________ for a population parameter.
What is "interval estimate".
Calculate the variance of the following sample:
5 8 3 4 5 3 9 7 8
Round final answer to hundredths.
5.19
An irate patient complained that the cost of a doctor's visit was too high. She randomly surveyed 20 other patients and found that the mean amount of money they spent on each doctor's visit was $44.80 with a standard deviation of $3.53. What assumption must be made in order to construct a 95% CI for the population mean?
What is "normally distributed"?
What condition has to be met in order for us to construct a confidence interval for a population proportion?
n*p-hat and n*q-hat must both be greater than or equal to 5
Find the left and right Chi-square values for a 99% CI with a sample size of 6
What is 0.412 and 16.750
When a 99% confidence interval is calculated instead of a 95% CI, assuming all other factors remain the same, the margin of error will be a) larger b) smaller c) the same d) cannot be determined
What is a) larger
The mean gestational length of a sample of 208 horses is 343.7 days, with a standard deviation of 10.4 days. The data set has a bell-shaped distribution.
Gestational lengths below _____ days would be unusually low.
What is 322.9 days?
The average weight of 40 randomly selected mini-vans was 4150 pounds. The population standard deviation was 480 pounds. Find the 99% CI of the population mean weight of the minivans. Round final answers to the nearest tenth.
What is 3954.2 < u < 4345.8
A recent study of 75 workers found that 53 people rode the bus to work each day. Find the 95% CI for the proportion of all workers of all workers who rode the bus to work. Round final answers to 3 decimal places.
What is 0.604 < p < 0.810
A sample of 25 novels has a standard deviation of 9 pages. Find the 95% CI of the population standard deviation. Assume the number of pages is normally distributed.
What is 7.0 < sigma < 12.5
A business wants to estimate the mean age of its customers. If they want to be 90% confident that the sample mean is within 1/2 year of the population mean, what is the minimum sample size the company should use? Assume the population standard deviation is about 8 years.
What is 689.
The weights of ice cream cartons are normally distributed with a mean weight of 10 ounces and a standard deviation of 0.5 ounce.
Find the weight that corresponds to the 72nd percentile.
What is 10.29 ounces?
An irate patient complained that the cost of a doctor's visit was too high. She randomly surveyed 20 other patients and found that the mean amount of money they spent on each doctor's visit was $44.80 with a standard deviation of $3.53. Assume the population is normally distributed. Find the 95% CI for the population mean.
What is $43.15 < u < $46.45
In a study of 150 accidents that required treatment in an emergency room, 36% involved children under 6 years of age. Find the 90% CI of the true proportion of accidents that involve children under the age of 6. Round final answers to 3 decimal places.
What is 0.296 < p < 0.424?
The maximum wind speeds (in knots) of 13 randomly selected hurricanes that have hit the U.S. mainland are listed below. Construct a 95% confidence interval for the population standard deviation. Assume wind speeds are normally distributed.
70 85 70 75 100 100 110 105 130 75 85 75 70
What is (13.6, 31.3) knots?
he weights of ice cream cartons are normally distributed with a mean weight of 10 ounces and a standard deviation of 0.5 ounce.
You randomly select 25 cartons. What is the probability that the mean weight is greater than 10.21 ounces?
What is 0.0179?
In a hospital, a sample of 8 weeks found that an average of 438 patients was treated in the emergency room each week, and the standard deviation was 16 patients. Find the 99% CI for the true mean.
What is "this problem can't be worked because n is less than 30 and we don't know that the weekly number of ER patients is normally distributed"?
You are running a political campaign and wish to estimate, with 98% confidence, the proportion of registered voters who will vote for your candidate. Your estimate must be accurate within 2% of the true population. Find the minimum sample size needed.
What is 3394 registered voters.
A sample of 1200 adults yielded a confidence interval of (0.685, 0.735) for the population proportion. To the nearest tenth of a percent, find the level of confidence.
What is 94.4%.
In a restaurant, a study is found that 22% of all patrons smoked. If the seating capacity of the restaurant is 75 people, find the mean, variance, and standard deviation of the number of smokers.
mean (mu) = 16.5
variance (sigma2)=12.87
standard deviation (sigma)=3.59