问题如下：
An analyst gathers the following information for an equal-weighted index comprised of assets Able, Baker, and Charlie:
The total return of the index is:
选项：
A.5.0%.
B.7.9%.
C.11.4%.
解释：
C is correct.
The total return of an index is calculated on the basis of the change in price of the underlying securities plus the sum of income received or the sum of the weighted total returns of each security. The total return of Able is 27.5 percent; of Baker is 0 percent; and of Charlie is 6.7 percent:
Able: (12 – 10 + 0.75)/10 = 27.5%
Baker: (19 – 20 + 1)/20 = 0%
Charlie: (30 – 30 + 2)/30 = 6.7%
An equal-weighted index applies the same weight (1/3) to each security’s return; therefore, the total return =1/3 × (27.5% + 0% + 6.7%) = 11.4%.
[(12 – 10 + 0.75) + (19 – 20 + 1)+(30 – 30 + 2)] / (10+20+30) 这样直接相加算出来是7.9%，看了很久没弄懂自己思路哪里错了，希望可以解析一下，谢谢
