Example 7.12. Lengths of Children's Animated Films

The lengths (in minutes) of a random selection of popular children's animated films are listed below. Assume the variable is normally distributed. Estimate the population variance and standard deviation in length of children's animated films with 99% confidence.

93

83

76

92

77

81

78

100

78

76

75

Solution:

Find the variance using technology.s2=____________

d.f. =_________

=__________,2=____________, and1 -2=__________

Findleft2=_________andright2=_____________

Substitute into the formula:

n-1s2right2<2<n-1s2left2

Now, take the square root of each side to find the confidence interval about the standard deviation: