A mobile phone manufacturer wishes to estimate how frequently their customers buy a new phone. They conduct a sample of 22 customers, and find that the sample mean is 1.9 years, with a sample standard deviation of 1.2 years. What is the upper value of a 90% confidence interval estimating the population mean? O 2.28 years O 2.30 years O 2.32 years O 2.34 years O 2.36 years

The distribution of study times for first year students follows a Normal distribution with standard deviation σ = 78 minutes. Suppose a sample of 452 students found that the mean study time for these students was x¯= 192 minutes per week. Use this to find a 95% confidence interval to estimate the mean study time for all students. We are 95% confident that the mean study time for first year students is between _____minutes and _____ minutes

83 students are asked in a survey how many hours they work during a week. Their responses have a mean of 19 hours and a standard deviation of 2 hours. Find the margin of error for a 80 % confidence interval. Round your answer in two decimal places

A random sample of 9 fields of rye has a mean yield of 39.4 bushels per acre and standard deviation of 4.09 bushels per acre. Determine the 95% confidence interval for the true mean yield. Assume the population is approximately normal. Step 2 of 2:  Construct the 95% confidence interval. Round your answer to one decimal place.

Suppose that an accounting firm does a study to determine the time needed to complete one person's tax forms. It randomly surveys 50 people. The sample mean is 22.7 hours. There is a known standard deviation of 8 hours. The population distribution is assumed to be normal. Round answers to 3 decimal places. a. Find the following: OT 005 O n b. Construct a 90% confidence interval for the population mean time to complete tax forms. o State the confidence interval. o Calculate the error bound. c. Suppose that the firm decided that it needed to be at least 99% confident of the population mean length of time to within one hour. How would the number of people the firm surveys change? Select an answer

If a school district takes a random sample of 56 Math SAT scores and finds that the average is 488, and knowing that the population standard deviation of Math SAT scores is intended to be 100. Find a 99% confidence interval for the mean math SAT score for this district._____<μ<_____

Suppose you take a random sample of n = 80 Douglas College students and ask each student their age. You find that the mean age of students in this sample is X = 22.0375 years and the sample standard deviation is s = 3.2014 years.  Fill in the blanks (rounding to four decimal places):  The 95% confidence interval for the mean age μ of all Douglas College students is from ______ years to ______ years.

you measure the weights of a random sample of twenty-five people. The sample mean is 60 kg. Suppose that the mean weights of people follow a normal distribution with an unknown mean and standard deviation of 5 kg. You compute a 95% confidence interval for μ. The 95% confidence interval for μ is?

The annual earnings of 13 randomly selected computer software engineers have a sample standard deviation of $3700. Assume the sample is from a normally distributed population. Construct a confidence interval for the population variance σ2 and the population standard deviation σ.Use a 95% level of confidence. Interpret the results. What is the confidence interval for the population variance σ2​?

Tina catches a 14-pound bass.  She does not know the population mean or standard deviation.  So she takes a sample of five friends and they say the last bass they caught was 9, 12, 13, 10, and 10 pounds.  Find the t and calculate a 95% (α = .05) confidence interval.