prep pp-ps1完整详解版的175题 题目全了，外加求助

行走钢丝

就是那个台湾朋友支持的数学prep详解版，其中的PP-PS1的选项后面是空的，解释也没有，我今天模考做到了这道题，就把它补了出来：
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
恩，选项是这样子了，可惜我模考做错了，题目都没看懂，郁闷，哪位大侠帮忙讲讲？不胜感激！含泪等。。。

   哦哦，忘了，正确答案是C

junyihuo

100 units of Country R's currency 是100块人民币或100块美元的意思

the average (arithmetic mean) of 100 units of Country R's currency and 1 percent of one's annual income是1/2 ×（100 + 1% I）

所以公式是2%I + 1/2 ×（100 + 1% I），化简后是C

我看到100 units of 的时候也没有读懂，按自己猜的意思算的，

行走钢丝

哦，这样我就明白了！

我不知怎么的就把currency想成汇率。。。哎。。。还纳闷半天。

谢谢MM咯！