A poll of 75 randomly selected college students showed that the students spent an average of $230 on textbooks per session. Assume from past studies that the standard deviation is $55. Find a 99% confidence interval for the amount of money spent by students on textbooks.

1. Find the sample statistics and z-score.

n = __________

x = __________

= __________

z = __________

1. Calculate the margin of error.

1. Construct the confidence interval.

Executives at a music label surveyed 125 people who actively download music and found that the listeners have an average of 740 songs downloaded to their electronic devices. Assume a standard deviation of 86 songs. Find a 95% confidence interval for the amount of songs on the electronic device of someone who actively downloads music.

1. Find the sample statistics and z-score.

n = __________

x = __________

= __________

z = __________

1. Calculate the margin of error.

1. Construct the confidence interval.

A company gives 4-hour boat tours for a dolphin watch. On 30 tours, the time between first leaving the dock to sighting a dolphin averaged 125 minutes. Assume a normal distribution with a standard deviation of 28 minutes. Find a 90% confidence interval for the mean time until the first dolphin sighting of all tours.

1. Find the sample statistics and z-score.

n = __________

x = __________

= __________

z = __________

1. Calculate the margin of error.

1. Construct the confidence interval.

1. You are testing the reliability of a thermometer. Your manager asks you to conduct an experiment with results that are accurate to 0.05 degree with 95% confidence. If = 0.8, how many measurements are needed?

1. Executives at a car dealership want to estimate the average age of their customers before making a television commercial. They want to be 90% confident that the mean age is 2 years of the sample mean. If the standard deviation from a previous study is 12 years, how large should the sample be?