An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 98% confidence interval  for the population mean of all bulbs produced by this firm.

The newest model of a car battery from a popular brand is supposed to have a lifetime of  60  months, but the lifetime varies slightly from battery to battery. It is known that the population of all lifetimes (in months) of this model of car battery is approximately normally distributed. You are a product reviewer who wants to estimate the standard deviation for this population with a random sample of  22  car batteries. Follow the steps below to construct a  99%  confidence interval for the population standard deviation of all lifetimes of this model of car battery. (If necessary, consult a list of formulas.) (a)Click on "Take Sample" to see the results from the random sample. Take Sample Number of carbatteries Sample mean Sample standard deviation Sample variance 22 57.16 0.38 0.1444   To find the confidence interval for the population standard deviation, first find the confidence interval for the population variance. Enter…

The president of a large university wishes to compare the standard deviation of the ages of students presently enrolled to previous years. The distribution of ages has been approximately normal. Find the 90% confidence interval for the population standard deviation of the student ages of the University. A random sample of 20 university students has a standard deviation of 6.1 years in a mean of 23.8 years what is the confidence interval of the population standard deviation?

The newest model of a car battery from a popular brand is supposed to have a lifetime of  60  months, but the lifetime varies slightly from battery to battery. It is known that the population of all lifetimes (in months) of this model of car battery is approximately normally distributed. You are a product reviewer who wants to estimate the standard deviation for this population with a random sample of  22  car batteries. Follow the steps below to construct a  99%  confidence interval for the population standard deviation of all lifetimes of this model of car battery. (If necessary, consult a list of formulas.) (a)Click on "Take Sample" to see the results from the random sample. Take Sample Number of carbatteries Sample mean Sample standard deviation Sample variance           To find the confidence interval for the population standard deviation, first find the confidence interval for the population variance. Enter the values…

A trial study suggest that the standard deviation for the half life for the drug chlordiazepoxide is 8 hours. With 99% confidence, find the sample size needed to determine the mean half life for the drug with a margin of error of 3 hours.

A non-symmetric dataset has a mean of 200 and a standard deviation of 15.  Find an upper bound for the proportion of data points that are either greater than 230 or less than 170.

An agricultural researcher plants 14 plots with a new variety of corn. The average yield for these plots is X = 155 bushels per acre. Assume that the yield per acre for new variety of corn follows a normal distribution with unknown mean and a calculated sample standard deviation s = 10 bushels. A 90% confidence interval for the unknown mean is

A study of 22 goats reveals that the average length of a goat’s tail is 6.3 inches. If the standarddeviation is known to be 1.2 inches find a 95% confidence interval for the mean tail length.

A ecologist wishes to estimate the mean lifespan for a specific species of bird. Assume that bird lifespan is normally distributed and that each bird's lifespan is independent of all others. The researcher analyzes a random sample of n=7 deceased birds to find out how long they lived for. It is found that the mean lifespan in the sample is y= 5 4 years with standard deviation s=13 years. Choose the correct formula for a 95% confidence interval for the true mean lifespan. X± to.975,n O xt to.975,n-1 n-1 O none of these X+ Z0.975 O x+ to.975,n-1' O xt to.975,n-15

A researcher collected sample data for 19 middle-aged women. The sample had a mean serum cholesterol level (measured in milligrams per one hundred milliliters) of 191.5, with a standard deviation of 6.5. Assuming that serum cholesterol levels for middle-aged women are normally distributed, find a 95% confidence interval for the mean serum cholesterol level of all women in this age group. Give the lower limit and upper limit of the 95% confidence interval. Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.  lower limit ____ Upper Limit ____