问题如下：
An analyst gathers the following information for an equal-weighted index comprised of assets Able, Baker, and Charlie:
The price return of the index is:
选项：
A.1.7%.
B.5.0%.
C.11.4%.
解释：
B is correct.
The price return is the sum of the weighted returns of each security. The return of Able is 20 percent [(12 – 10)/10]; of Baker is –5 percent [(19 – 20)/20]; and of Charlie is 0 percent [(30 – 30)/30]. The price return index assigns a weight of 1/3 to each asset; therefore, the price return is 1/3 × [20% + (–5%) + 0%] = 5%.
考点：Methods of index construction
这道题让我们计算的是等权重构建方法下的指数的price return，所以我们首先要区分price return和total return，计算price return不需要包括期间的收益即股息。第二，这里是等权重的构建方法，等权重相当于每只股票买了相同的金额，那么我们就先计算每种股票的收益率再除以股票种类。
老师Equal-weighted是每一个成分股都买相同的金额，我假设每个股票买1块钱的，然后期初是3/(1/10+1/20+1/30，期末应该是3/(1/12+1/19+1/30)。然后用期末除以期初的不就是增长率吗？我这样算错在哪里啊？谢谢老师
