1. Assuming that the following sample is taken from a normal distribution, compute the 90% confidence interval for the population mean.

Dataset:

67.2

82.2

59.7

54.9

77.7

48.1

95.2

63.8

96.7

87

2. A telecommunication company wants to estimate the mean length of time (in minutes) that 18- to 24- year-olds spend text messaging each day. In a random sample of fifty-eight 18- to 24-year-olds, the mean length of time spent text messaging was 29 minutes. From past studies, the company assumes that is 4.5 minutes and that the population of times is normally distributed.

• Compute a 99% confidence interval for the population mean time that 18- to 24-year-olds spend text messaging each day.
• Interpret the confidence interval found in part a.
• What does the phrase "99% confidence" refer to in this context?

3. The following table shows the results of a survey in which 1017 adults from the United States, 1060 adults from Italy, and 1126 adults from Great Britain were asked the question: "Does climate change pose a large threat to the world?"

Country	Percentage That Responded "Yes"
United States	27%
Italy	49%
Great Britain	31%

Construct and interpret a 98% confidence interval for

• The population proportion of adults from the United States who say that climate change poses a large threat to the world.
• The population proportion of adults from Italy who say that climate change poses a large threat to the world.
• The population proportion of adults from Great Britain who say that climate change poses a large threat to the world.

4. To compare the braking distance for two types of tires, a safety engineer conducts 45 braking tests for each type. The results of the tests are given below.

Tire Type	Mean	Standard Deviation
Tire A	42 feet	2.9 feet
Tire B	45 feet	3.1 feet

1. Construct a 98% confidence interval for the difference in the population mean braking distance of the two tire types.
2. Based on the interval in part a., does it appear that there is a statistically significant difference between the two population means? Explain.