[求助]PREP-PS1-175 题目怎么翻译?

实在搜索不到,只好发一贴了.先谢过!

请教哪位高人这道题怎么翻译啊?实在理解不了求哪个和哪个的平均值.怎么得到答案C的?

175.
                18356-!-item-!-187;#058&011490

Before being simplified, the instructions for computing income tax in Country R were to add 2 percent of one's annual income to the average (arithmetic mean) of 100 units of Country R's currency and 1 percent of one's annual income.  Which of the following represents the simplified formula for computing the income tax, in Country R's currency, for a person in that country whose annual income is I ?

(A)  50+I/200

(B)  50+(3I)/100

(C)  50+I/40

(D)  100+I/50

(E)  100+(3I)/100

KEY:C

the instructions for computing income tax in Country R were to add 2 percent of one's annual income to the average (arithmetic mean) of 100 units of Country R's currency and 1percent  of one's annual income

意思是 tax是把2 percent 的个人年收入再加上 100个单位的国家货币（就是100块钱）和1percent 个人年收入的算术平均值

个人年收入是I ，所以是0.02I+（100+0.01I）/2

多谢!我脑子秀逗了，居然不知道平均数去除几了.