OG12 PS163

小鬼和灵

163. 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 has
available to spend will be equal to half the amount that
he spends this year?

for each dollar that he saves
this year, he will have 1 + r dollars available to spend.
完全不懂这句话……求解！

小鬼和灵

自己顶一下

alexandrahs

之前我也不明白这个题意。。。
意思是，每存1美元明年就可以有1+r美元可以用。设存了a.则明年有a(1+r)可以花。设今年收入为x,今年就花了x-a.
根据题意，列式a(1+r)=1/2（x-a), 解到a(3+2r)=x时，因为求a/x=? ,所以就等于
1/3+2x

对不？？

小鬼和灵

恩 谢谢！