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Lec20-21-ex

# Lec20-21-ex - 7.15(a df = 14 t = 2.145(b df = 24 t =...

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7.15 (a) df = 14, t * = 2 . 145. (b) df = 24, t * = 2 . 064. (c) df = 24, t * = 1 . 711. (d) For a given confidence level C , t * (hence the margin of error m ) decreases as sample size n increases. Given n , t * increases as the confidence level C increases. 7.21 (a) df = 23. (b) 2 . 177 < t < 2 . 500. (c) For the two-sided H a , we double the upper-tail probabilities to find the p -value: 0 . 02 < p < 0 . 04. (d) t = 2 . 40 is significant at the level α = 0 . 05, but not at the level α = 0 . 01. 7.24 (b) ¯ x = 43 . 17, s = 4 . 4149, n = 20, s/ n = 0 . 9872. For df = 19, the critical value with α/ 2 = 0 . 025 is t * = 2 . 093, hence the margin of error is m = 2 . 0662. (c) The 95% CI is (41 . 1038 , 45 . 2362). 7.32 (a) and (b) The mean for paired differences is ¯ x = 4 . 73125 with SD s = 1 . 7457. (c) SE

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Lec20-21-ex - 7.15(a df = 14 t = 2.145(b df = 24 t =...

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