NO.PZ2015122802000051
问题如下：
An analyst gathers the following data for an equally-weighted index:
The return on the index over the period is:
选项：
A.
4.2%.
B.
6.8%.
C.
7.1%.
解释：
C is correct.
With an equal-weighted index, the same amount is invested in each security. Assuming $1,000 is invested in each of the three stocks, the index value is $3,000 at the beginning of the period and the following number of shares is purchased for each stock:
Security A: 50 shares
Security B: 20 shares
Security C: 38.46 shares.
Using the prices at the beginning of the period for each security, the index value at the end of the period is
$3,213.8: ($22 × 50) + ($48 × 20) + ($30 × 38.46). The price return is $3,213.8/$3,000 – 1 = 7.1%.
考点：等权重指数计算收益率
等权重有两种思路来计算，一种方式也是李老师上课讲的（直接计算收益率之和除以3）。还有一种就是这道题的思路，它是从等权重最本源的含义出发的：假设每只股票买相同的金额，因此每只股票在指数中的权重是相等的。两种方法的结果是一致的。但解析做法没有咱们上课讲的直接计算收益率之和除以3简便。
简单说一下，假设每只股票没相同的金额1000, 因此期初三只股票价值=1000*3=3000（这只是题目假设，可以是任意金额，10,100,1000任何数字都可以），那么期初A股票可以买1000/20=50只，B可以买20只，C可以买38.46只股票。到了期末由于三只股票价格发生变化，A价值=50*22=1100，B价值=20*48=960， C价值=38.46*30=1153.8，所以期末三只股票的价值=1100+960+1153.8=3213.8
因此该股指的收益率就等于期末价值除以期初价值减1= $3213.8/$3,000 – 1 =7.1%.
如题，5，20，38.46是哪里来的？
