BackA technician wants to estimate the average battery life of a new type of smart phone, so he tests 8 randomly selected phones & records the data below. Assuming battery life has a normal dist, make a 90% conf. int. for the mean battery life.
Age of Death-Row InmatesIn 2002, the mean age of an inmate on death row was 40.7 years, according to data from the U.S. Department of Justice. A sociologist wondered whether the mean age of a death-row inmate has changed since then. She randomly selects 32 death-row inmates and finds that their mean age is 38.9, with a standard deviation of 9.6. Construct a 95% confidence interval about the mean age. What does the interval imply?
What requirements must be satisfied in order to construct a confidence interval about a population mean?
[DATA] Family Size A random sample of 60 married couples who have been married 7 years was asked the number of children they have. The results of the survey are as follows:
Note: x̄ = 2.27, s = 1.22.
b. Compute a 95% confidence interval for the mean number of children of all couples who have been married 7 years. Interpret this interval.
[DATA] Family Size A random sample of 60 married couples who have been married 7 years was asked the number of children they have. The results of the survey are as follows:
Note: x̄ = 2.27, s = 1.22.
c. Compute a 99% confidence interval for the mean number of children of all couples who have been married 7 years. Interpret this interval.
Long Life? In a survey of 35 adult Americans, it was found that the mean age (in years) that people would like to live to is 87.9 with a standard deviation of 15.5. An analysis of the raw data indicates the distribution is skewed left.
b. Construct and interpret a 95% confidence interval for the mean.
In Exercises 27–30, find the critical values and for the level of confidence c and sample size n.
c = 0.99, n = 10