**Read** Chapter 9

**Do** the following problems:

**9.2**

**9.3**

**9.3'** Use the data in Problem 9.3 to provide a 90% CI for the population mean, assuming that the population
standard deviation is unknown and has to be estimated
from the data.

**9.5**

**9.8**

**9.12**

**9.14**(Hint: Estimate the standard deviation conservatively by
range/4.)

**9.15**

**Additional Problem:** A growing concern for educators in the
United States is the number of teenagers who have part-time jobs while
they attend high school. It is generally believed that the amount of
time teenagers spend working is deducted from the amount of time
devoted to school work. To investigate this problem, a school guidance
counselor took a random sample of 200 15-year-old high school and
asked how many hours per week each worked at a part-time job. The
results were recorded and he found that the sample mean and sample
standard deviation were `xbar = 5.125` and `s=3.310`.
Estimate with 95% confidence the mean amount of time all 15-year-old
high school students devote per week to part-time jobs.