Solution HW5
1. A confidence interval estimate is desired for the gain in a circuit on a semiconductor device. Assume
that gain is normally distributed with sd.=20.
a) Find a 95% CI for µ when n =10 and
b) Find a 95% CI for µ when n =25and
c) Find a 99% CI for µ when n =10 and
d) Find a 99% CI for µ when n =25 and
e) How does the length of Vis computed above change with the changes in sample size and
confidence level?
2. The sugar content of the syrup in canned peaches is normally distributed. A random sampling of n=10
cans yields a sample standard deviation of s=4.8 mg. Calculate a 95% two-sided confidence interval for 
3. The 2004 presidential election exit polls from the critical state of Ohio provided the following results.
There were 2020 respondents in the exit polls and 768 were college graduates. Of the college graduates,
412 votes for George Bush.
a) Calculate a 95% confidence interval for the proportion of college graduates in Ohio that voted
for George Bush?
b) Calculate a 95% lower confidence bound for the proportion of college graduates in Ohio that
voted for George Bush?