※ 引述《az710075 (~~)》之銘言：
: 題目
: A population mean is being estimated based on a sample of size 49.
: The sample mean is 95, and the sample standard deviation is 21.
: a. Construct CI95.
: 這有算出來是
: CI95=(88.97,101.03)
: b. Assume that another sample has a standard deviation of 21 (or very
: close to 21). what sample size is required to have a CI95 that does
: not exceed seven points in width? (Hint: Estimate the critical value
: needed based on the information from the solution of part a.)
: b小題解不出來，不知如何算出sample size
: 再麻煩大大解答，謝謝
是指至少需要多少樣本才能建構出寬不超過 0.7 單位的 CI95 嗎?
(a) 小題的 CI 寬 = 95正負 6.03，如果要做出更窄的 CI 就需要更多樣本
基於 (a) 小題可以知道 (b) 小題的樣本數 n > 49，由 CLT 知
進似信賴區間的寬為 正負 z_0.025 * s/sqrt(n) = 1.96 * 21/sqrt(n) 希望 <= 0.7
解得 n >= (1.96 * 21 / 0.7)^2 = 3457.4 = 3458
如果搞錯題意，寬度要求是 7 的話，那 (1.96*21 / 7)^2=34.57=35
做參考嚕~
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