题目
In Millford, of the residents own a bicycle. A random sample of 160 residents is selected.
Use a suitable approximation to find the probability that more than 120 of these residents own a bicycle.
题目中文翻译
在 Millford, 的居民拥有自行车。随机抽取 160 名居民作为样本。
使用适当的近似方法,求这些居民中超过 120 人拥有自行车的概率。
原卷通用作答要求
Answer all questions. You should use a calculator where appropriate.
You must show all necessary working clearly; no marks will be given for unsupported answers from a calculator.
Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place for angles in degrees, unless a different level of accuracy is specified in the question.
请回答所有题目。适当时应使用计算器。必须清楚展示所有必要的计算过程;仅给出计算器答案而没有过程,不予评分。除非题目另有精度要求,非精确数值答案保留 3 位有效数字,以度为单位的角度保留 1 位小数。
解答
解法一
思路
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人数服从二项分布,可用正态近似。超过120即至少121,连续性修正后的下界是120.5。
答题过程
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Let be the number owning a bicycle. Since and are both greater than 5, use , where .
With a continuity correction,