数学题目及解析
A group of 5,000 investors responded to a survey asking whether they owned stocks and whether they owned bonds. Of the group, 20 percent responded that they owned only one of the two types of investments. If r is the number of investors in the group who owned stocks but not bonds, which of the following represents the number of investors in the group who owned bonds but not stocks, in terms of r?
A. 5,000 - r B. 1,000 - r
C. r - 1,000 D. 1,000r
E. (0.2)(5,000 - r)
【答案】B
【思路】
共5000人，其中20%即1000人有股票或者债券之一，r個人只有股票沒有债券，那么只有债券没有股票的就是1000-r個人，选B。