A phone company has conducted a study of the time its clients spend talking on their cellular phones each day. For a sample of 10 clients the company has obtained a sample standard deviation of 13.3 minutes. We assume that the talk time follows a normal distribution. The confidence interval at the 90% level for the standard deviation of the talk time in the population is:

A phone company has conducted a study of the time its clients spend talking on their cellular phones each day. For a sample of 10 clients the company has obtained a sample standard deviation of 13.3 minutes. We assume that the talk time follows a normal distribution. The confidence interval at the 90% level for the standard deviation of the talk time in the population is:

MATLAB: An Introduction with Applications

6th Edition

ISBN:9781119256830

Author:Amos Gilat

Publisher:Amos Gilat

Chapter1: Starting With Matlab

Section: Chapter Questions

Problem 1P

See similar textbooks

Similar questions

You measure 25 randomly selected textbooks' weights, and find they have a mean weight of 73 ounces. Assume the population standard deviation is 5.8 ounces. Based on this, construct a 95% confidence interval for the true population mean textbook weight.
Insurance Company A claims that its customers pay less for car insurance, on average, than customers of its competitor, Company B. You wonder if this is true, so you decide to compare the average monthly costs of similar insurance policies from the two companies. For a random sample of 13 people who buy insurance from Company A, the mean cost is $150 per month with a standard deviation of $19. For 9 randomly selected customers of Company B, you find that they pay a mean of $157 per month with a standard deviation of $16. Assume that both populations are approximately normal and that the population variances are equal to test Company A's claim at the 0.05 level of significance. Let customers of Company A be Population 1 and let customers of Company B be Population 2. Step 1 of 3: State the null and alternative hypotheses for the test. Fill in the blank below. Ho: M₁ = μ₂ Ha:M₁ •H₂
Find the 95% confidence interval for the variance and standard deviation for the time it takes a state police inspector to check a truck for safety if a sample of 21 trucks has a standard deviation of 5.2 minutes. Assume the variable is normally distributed.
The standard deviation, S, for the annual medical cost of 24 households was found to equal $1689 find a 95% confidence interval for the standard deviation of the annual medical cost for all households. Assume medical costs are normally distributed.
In a recent sample of 89 used cars sales costs, the sample mean was $6,225 with a standard deviation of $3,151. Assume the underlying distribution is approximately normal. Which distribution should you use for this problem? Construct a 95% confidence interval for the population mean cost of a used car.
In a random sample of 5 mobile devices, the mean repair cost was $60.00 and the standard deviation was $12.00. Assume the population is normally distributed and use a t-distribution to find the margin of error and construct a 95% confidence interval for the population mean. Interpret the results.
Suppose a sample of 30 students are given an IQ test. The sample has a standard deviation of 12.23 points. Assuming IQ test score follow a normal distribution, suppose the researcher wishes to obtain a 90% confidence interval for the population standard deviation.
Insurance Company A claims that its customers pay less for car insurance, on average, than customers of its competitor, Company B. You wonder if this is true, so you decide to compare the average monthly costs of similar insurance policies from the two companies. For a random sample of 15 people who buy insurance from Company A, the mean cost is $154 per month with a standard deviation of $13. For 11 randomly selected customers of Company B, you find that they pay a mean of $159 per month with a standard deviation of $16. Assume that both populations are approximately normal and that the population variances are equal to test Company A’s claim at the 0.02 level of significance. Let customers of Company A be Population 1 and let customers of Company B be Population 2. Step 2 of 3 : Compute the value of the test statistic. Round your answer to three decimal places.
Dr. Graham is interested in determining if middle-aged adults use text messaging more or less frequently than the general population. Dr. Graham collects information on text messaging from a random sample of 50 adults ages 25 to 44. Dr. Graham finds that these individuals send or receive an average of 68 text messages per day. Using the population mean (and standard deviation) of 41.5 texts per day (34 texts per day), determine whether adults in this age group use text messaging more than the general public.
Insurance Company A claims that its customers pay less for car insurance, on average, than customers of its competitor, Company B. You wonder if this is true, so you decide to compare the average monthly costs of similar insurance policies from the two companies. For a random sample of 1313 people who buy insurance from Company A, the mean cost is $151$⁢151 per month with a standard deviation of $16$⁢16. For 99 randomly selected customers of Company B, you find that they pay a mean of $158$⁢158 per month with a standard deviation of $19$⁢19. Assume that both populations are approximately normal and that the population variances are equal to test Company A’s claim at the 0.050.05 level of significance. Let customers of Company A be Population 1 and let customers of Company B be Population 2. Step 2 of 3: Compute the value of the test statistic. Round your answer to three decimal places.
A manufacturer advertises that the average life of batteries produced by his firm is at least 12 months. The consumer board disagrees, and claims that the average life of the batteries is less than 12 months. The consumer board test a random sample of 9 batteries and find that the mean life is 10.6 months with a standard deviation of 2. The consumer board's alternative hypothesis is: A. The average life of the population of batteries is 12 months. B. The average life of the population of batteries is less than 12 months. C. The average life of the population of batteries is more than 12 months. D. The average life of the population of batteries is at least 12 monthsThe manufacturer of 'Road King' tyres claim that their tyres last an average of 70,000km or more. The Consumer Board suspects that this claim may be false (they have received some complaints) and decide to test the manufacturer's claim. The Consumer Board took a sample of size 500 from the population. They ran the…
Suppose we wish to calculate a 90% confidence interval for the average amount spent on books by freshmen in their first year at a major university. The interval is to have a margin of error of $2. Assume that the amount spent on books by freshmen has a normal distribution with a standard deviation of $30. How many observations are required to achieve this margin of error?