University of Florida
ESI 3770
Only the 1st five problems will be graded, any additional problems are for practice.
1. Suppose the lifetimes for two competing brands of tires are independent of each
other and approximately normal with unknown means but known variances
σ2
1 = 975 miles2 and σ2 2 = 965 miles2. We did some testing under controlled
conditions and have the following summar
...[Show More]
University of Florida
ESI 3770
Only the 1st five problems will be graded, any additional problems are for practice.
1. Suppose the lifetimes for two competing brands of tires are independent of each
other and approximately normal with unknown means but known variances
σ2
1 = 975 miles2 and σ2 2 = 965 miles2. We did some testing under controlled
conditions and have the following summary statistics:
n1 = 75
x ¯1 = 3251:4
n2 = 60
x ¯2 = 3274:7
Construct a 80% confidence interval for the difference in population means, µ1-µ2.
Solution: Using the formulas from class, we have
n1 = 75
x ¯1 = 3251:4
σ2
1 = 975
n2 = 60
x ¯2 = 3274:7
σ2
2 = 965
α = 0:2
zα=2 = 1:28
µ1 - µ2 2 x ¯1 - x ¯2 ± zα=2sσ n1 1 2 + σ n2 2 2
= [-30:203; -16:397]
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