[問題]天山7-28

[umum29]

This year Henry will save a certain amount of his income, and he will spend the rest. Next year Henry will have no income, but for each dollar that he saves this year, he will have 1+r dollars available to spend. In terms of r, what fraction of his income should Henry save this year so that next year the amount he was available to spend will be equal to half the amount that he spends this year?

答案為 1/(2r+3)

順道問問各位前輩 我現在做天山考題大概都會錯個5,6題.
這樣的水準在正式考試中大概可以得到怎樣的分數(就計量而言)?
謝謝大家的回答!!

[Pufa]

我印象中這題好像有人問過了。
設全部的薪水是Y，其中存了X下來，
2X(1+r)=Y-X
就可以求出答案了。

[umum29]

不好意思 我還是不太明白
我當初也是假設出 2(1+r)=Y-X這個式子
但 ,就題目所給的條件 我是否能知道X=1+r?(因為下一年度的花費等於上一年度的儲蓄)
而題目的fraction是否就是求出最後答案的倒數?

[shine822]

這題是 GWD 5-28 才對！！

http://www.formosamba.com/phpBB3/viewtopic.php?t=1547