1. A student randomly selects 10 CDs at a store. The mean
is 8:75 dollars with a standard deviation of 1:50: Construct a 95% con-
?dence interval for the population standard deviation, . Assume the
data are normally distributed
Solution
(n-1)s2/(Xu2) < 2 < (n-1)s2/(XL2)
Look up the chi square values from the tables
X0.9752 With n-1=9 degrees freedom = 2.7
X0.0252 With n-1=9 degrees freedom = 19.023
s2=1.52=2.25
9*2.25/19.023 < 2 < 9*2.25/2.7
1.0645 < 2 < 7.5
1.03 < < 2.74