请教PP1-PS题,弄不出算法耶~~

loveshin86

162.    7564-!-item-!-187;#058&005577

Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month.  The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save.  If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?

答案是:1/5

请高人指点吧~下面还有一提

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 ?

答案是:50+I/40

一样是搞不懂啦.希望有人能帮忙啦

flyakite8606

第一题，设fraction 为X，每月pay为１，列方程　12X=3(1-x),x=1/5

第二题，根据题目意思，formula等于　2%*I+(100+1%*I)/2 =50+I/40

loveshin86

可以解释一下为什么这么列吗?

2%*I+(100+1%*I)/2 ,因为题目的意思我也看不太懂,谢谢

flyakite8606

 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. 

意思就是说把２％的收入加上　１００元和１％收入的平均数啊

flyakite8606

希望我讲清楚了

loveshin86

完全了解啦,非常感谢!!