2. 外语
  3. A research scientist wants to study a certain attribute of dogs. It is estimated that approximately 5 percent of all dogs have t

A research scientist wants to study a certain attribute of dogs. It is estimated that approximately 5 percent of all dogs have t

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问题 A research scientist wants to study a certain attribute of dogs. It is estimated that approximately 5 percent of all dogs have this attribute. If the scientist wants to study a sample of N dogs having the attribute, approximately how many dogs should be screened in order to obtain the desired sample size?
选项 A、N/5.
B、5N.
C、20N.
D、105N.
E、120N.
答案C
解析 一科学家想研究狗的某种特性。据估计约有5%的狗具有这种特性。若这位科学家想把N只具有这种特性的狗作为一个样本来研究，那么为了得到期望的样本大小，大约需要筛选多少条狗?
解：本题的正确答案为(C)。设需筛选x条狗，则由题意可得：x×5％=N → x=20N
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