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Chapter 11 Free Response Anwers

# Chapter 11 Free Response Anwers - .217.021 2.262 10 ±...

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AP Statistics – Chapter 11: Practice Free Response Exam - ANSWERS 1. SINGLE-SAMPLE t a) Carry out a complete test to answer the questions posed . Hypotheses: H o : μ = 78.1 H a : μ < 78.1 x-bar = 59.59 and s=6.255 so 59.59 78.1 6.255 9 t - = = -8.88 and p = .00001 Conclusion: Since the p-value is extremely low, we can conclude that the percent of nitrogen in the atmosphere during the Cretaceous era was significantly less than today. b) Under what conditions is it acceptable to perform the test in part (a) on this data? Since the sample size is so small, we would need a normal distribution. It is also very important that the data be collected in a random manner. 2. MATCHED-PAIRS t a) Find a 95% confidence interval for the difference in fuel used ( discount name brand ). First compute the differences: Car # 1 2 3 4 5 6 7 8 9 10 Diff -0.12 -0.15 0.35 0.3 0.04 -0.36 0.08 0.12 -0.14 0.09 x-bar = .021 and s=.217, With df=9 and 95% confidence t*=2.262, so the interval is
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Unformatted text preview: .217 .021 2.262 10 ± = -.1342 to .1762 b) What does the interval suggest about mileage differences for the two fuel types? They may be equal since 0 is in the interval. Since the interval is partly negative, it is also possible that the mileage with the discount gas is better. 3. TWO-SAMPLE t . Let μ 1 = Nitrites, μ 2 = Control, Hypotheses: H o : μ 1 = μ 2 H a : μ 1 < μ 2 Sample sizes are large enough that normality is not an issue. We also expect that the samples are chosen randomly. ( 29 2 2 7880 8112 1115 1250 30 30 t-= + = -.759 and p = .226 Conclusion: Since the p-value is not very low, we fail to reject the null hypothesis. It does not appear that nitrites can significantly reduce the amount of bacteria in meat....
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