1) Find the critical value zc that corresponds to a 95% confidence level.
2) Construct and Interpret Confidence Intervals for the Population Mean:
A random sample of 40 students has a test score with x = 81.5 and s = 10.2. Construct the confidence
interval for the population mean, μ if c = 0.90.
3) The standard IQ test has a mean of 101 and a standard deviation of 16. We want to be 98% certain
that we are within 4 IQ points of the true mean. Determine the required sample size.
4) In order to efficiently bid on a contract, a contractor wants to be 95% confident that his error is less
than two hours in estimating the average time it takes to install tile flooring. Previous contracts indicate
that the standard deviation is 4.5 hours. How large a sample must be selected? 5) Find the critical value, tc for c = 0.99 and n = 10. 6) When 435 college students were surveyed,120 said they own their car. Find a point estimate for p,
the population proportion of students who own their cars.
7) A survey of 400 non-fatal accidents showed that 189 involved the use of a cell phone. Find a point
estimate for p, the population proportion of non-fatal accidents that involved the use of a cell phone. 8) A survey of 250 homeless persons showed that 17 were veterans. Find a point estimate p, for the
population proportion of homeless persons who are veterans. 9) Construct a 95% confidence interval for the population standard deviation σ of a random sample of
15 men who have a mean weight of 165.2 pounds with a standard deviation of 13.5 pounds. Assume the
population is normally distributed.
10) A student randomly selects 10 CDs at a store. The mean is $13.75 with a standard deviation of $1.50.
Construct a 95% confidence interval for the population standard deviation, σ. 11) Determine the sampling error if the grade point averages for 10 randomly selected students from a
class of 125 students has a mean of x = 1.8. Assume the grade point average of the 125 students has a
mean of μ = 2.4. 12) A random sample of 120 students has a test score average with a standard deviation of 9.2. Find the
margin of error if c = 0.98
