A set of solar batteries is used in a research satellite. The satellite can run on only one battery, but it runs best if more than one battery is used. The variance ?2 of lifetimes of these batteries affects the useful lifetime of the satellite before it goes dead. If the variance is too small, all the batteries will tend to die at once. Why? If the variance is too large, the batteries are simply not dependable. Why? Engineers have determined that a variance of ?2 = 23 months (squared) is most desirable for these batteries. A random sample of 30 batteries gave a sample variance of 15.2 months (squared). Using a 0.05 level of significance, test the claim that ?2 = 23 against the claim that ?2 is different from 23.

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A set of solar batteries is used in a research satellite. The satellite can run on only one battery, but it runs best if more than one battery is used. The variance ?2 of lifetimes of these batteries affects the useful lifetime of the satellite before it goes dead. If the variance is too small, all the batteries will tend to die at once. Why? If the variance is too large, the batteries are simply not dependable. Why? Engineers have determined that a variance of ?2 = 23 months (squared) is most desirable for these batteries. A random sample of 22 batteries gave a sample variance of 15 months (squared). Using a 0.05 level of significance, test the claim that ?2 = 23 against the claim that ?2 is different from 23. (f) Find a 90% confidence interval for the population variance. (Round your answers to two decimal places.) (g) Find a 90% confidence interval for the population standard deviation. (Round your answers to two decimal places.)

One professor who teaches statistics gave students one homework assignment. He asked students to find a two-variable data set and compute the Pearson correlation coefficient. One student found a data set: one variable is students' midterm test score in an introductory microeconomics class and total observations are 45 students; while the other one variable is also students' midterm test score in another introductory microeconomics class and total observations are 57 students. Both of these two classes were taught by the same instructor in spring 2018. Does this student's data set make sense? Why or why not? Discuss and explain your reasons. You must provide your statistical analysis and reasons.

A set of solar batteries is used in a research satellite. The satellite can run on only one battery, but it runs best if more than one battery is used. The variance σ2 of lifetimes of these batteries affects the useful lifetime of the satellite before it goes dead. If the variance is too small, all the batteries will tend to die at once. Why? If the variance is too large, the batteries are simply not dependable. Why? Engineers have determined that a variance of σ2 = 23 months (squared) is most desirable for these batteries. A random sample of 22 batteries gave a sample variance of 13.2 months (squared). Using a 0.05 level of significance, test the claim that σ2 = 23 against the claim that σ2 is different from 23. (a) What is the level of significance?   Find the value of the chi-square statistic for the sample. (Round your answer to two decimal places.) What are the degrees of freedom?   (f) Find a 90% confidence interval for the population variance. (Round your answers to two decimal…

A set of solar batteries is used in a research satellite. The satellite can run on only one battery, but it runs best if more than one battery is used. The variance σ2 of lifetimes of these batteries affects the useful lifetime of the satellite before it goes dead. If the variance is too small, all the batteries will tend to die at once. Why? If the variance is too large, the batteries are simply not dependable. Why? Engineers have determined that a variance of σ2 = 23 months (squared) is most desirable for these batteries. A random sample of 20 batteries gave a sample variance of 13.8 months (squared). Using a 0.05 level of significance, test the claim that σ2 = 23 against the claim that σ2 is different from 23. (a) What is the level of significance?State the null and alternate hypotheses. A. Ho: σ2 = 23; H1: σ2 ≠ 23 B. Ho: σ2 = 23; H1: σ2 < 23     C. Ho: σ2 = 23; H1: σ2 > 23 D. Ho: σ2 > 23; H1: σ2 = 23 (b) Find the value of the chi-square statistic for the sample. (Round…

Use the following information to answer the question.  A researcher wants to study different messaging platforms by collecting data on 40 individuals. Half of the individuals only use iMessage while the other half only use What's App. For the individuals who only used iMessage, they sent an average of 280 messages with a sample variance of 170 in the past week. For the individuals who only used What's App, they sent an average of 295 messages with a sample variance of 182 in the past week. Determine if there is a significant difference between the average messages sent between the two groups of individuals. Use a significance level of 1%. What is the null hypothesis? Group of answer choices A. The iMessage group on average sent more messages than the What's App group.   B. The iMessage group on average sent less messages than the What's App group.   C. There is no difference in the average number of messages sent between the two groups.   D. There is a difference in the average…

A set of solar batteries is used in a research satellite. The satellite can run on only one battery, but it runs best if more than one battery is used. The variance o of lifetimes of these batteries affects the useful lifetime of the satellite before it goes dead. If the variance is too small, all the batteries will tend to die at once. Why? If the variance is too large, the batteries are simply not dependable. Why? Engineers have determined that a variance of o2 23 months (squared) is most desirable for these batteries. A random sample of 30 batteries gave a sample variance of 15.4 months (squared). Using a 0.05 level of significance, test the claim that o? = 23 against the claim that o is different from 23. (f) Find a 90% confidence interval for the population variance. (Round your answers to two decimal places.) lower limit upper limit (g) Find a 90% confidence interval for the population standard deviation. (Round your answers to two decimal places.) lower limit months upper limit…

Actuaries use various parameters when evaluating the cost of a life insurance policy. The variance of the life spans of a population is one of the parameters used for the evaluation. Each year, the actuaries at a particular insurance company randomly sample 30 people who died during the year (with the samples chosen independently from year to year) to see whether the variance of life spans has changed. The life span data from this year and from last year are summarized below. Current Last Year Year x1 = 75.8 | x,= 76.2 si= 47.61 s3= = 92.16 (The first row gives the sample means and the second row gives the sample variances.) Assume that life spans are approximately normally distributed for each of the populations of people who died this year and people who died last year. Can we conclude, at the 0.05 significance level, that the variance of the life span for the current year, of, differs from the variance of the life span for last year, o,? Perform a two-tailed test. Then complete the…

Two coworkers commute from the same building. They are interested in whether or not there is any variation in the time it takes them to drive to work. They each record their times for 20 commutes. The first worker's times have a variance of 12.1. The second worker's times have a variance of 16.9. The first worker thinks that he is more consistent with his commute times and that his commute time is shorter. Test the claim at the 10% level. What is s1 in this problem? What is s2 in this problem?