885 Test B 15 相对值&绝对值

yzlinlin

19.    The U.S. census is not perfect: thousands of Americans probably go uncounted. However, the basic statistical portrait of the nation painted by the census is accurate. Certainly some of the poor go uncounted, particularly the homeless; but some of the rich go uncounted as well, because they are often abroad or traveling between one residence and another.
Which of the following is an assumption on which the argument above depends?
(A) Both the rich and the poor have personal and economic reasons to avoid being counted by the census.
(B) All Americans may reasonably be classified as either poor or rich.
(C) The percentage of poor Americans uncounted by the census is close to the percentage of rich Americans uncounted.
(D) The number of homeless Americans is approximately equal to the number of rich Americans.
(E) The primary purpose of the census is to analyze the economic status of the American population.

答案C。排除ABE后在C和D之间取舍时，选C依据是觉得D有些荒谬。 大家是如何分析的？从何判断？the basic statistical portrait of the nation ？
不好意思，弱问题。

miejue

这里D的错误在于它把比较的对象弄错了

这里比较的是uncounted的百分比 举个例子可能比较容易理解

census共500人 其中穷人400人（含homeless的100人） 富人100人 所以portrait的结果是穷人：富人＝4：1

根据C 如果穷人中没有计算在内的占25％ 富人也有25％没有算在内 portrait的结果还是穷人：富人＝300：75＝4：1

根据D 上面的条件符合它的假设 但是如果此时没有计算在内的穷人有200人 则portrait的结果就是穷人：富人＝200：300＝2：3了

yzlinlin

谢谢miejue!

你的例子深入浅出，要不明白都难。

不过，你为什么把未统计的200穷人加到富人里呢？我觉得题中未涉及呀。

我觉得是否应该这样：接上例，假设D，则如果穷人、富人各少统计50人，那么比例由4：1 变为350：50=7：1。