[求助]8月JJ 157

ninaluan

157.

1000美元存银行。复利R半年计息一次。问，如果一年末利息收入是80.56美元，则R的可能取值是多少。
A  5<R<6.  

B 6<R<7  

C 7<R<8  

D 8<R<9  

E 9<R<10

horsefish:C
1000(1+r%0.5)^2-1000=80.56,请问这么列式子对吗? 或是有什么简单算法得出C?谢谢!

yayajiaojeff

求通法的话则horsefish's answer is perfect. But if you want to find another way, 用代入法。

becuase the interest income is slightly above 80.00, then pick 8% first, semi-annual compound. You will find the interest income will be 81.6, $1.04 higher than 80.56. So the choice must be just slighthly lower than 8%. So choose C.

流沙

81.6是怎么得到的？我怎么也算不出来，5555～～～～

ninaluan

以下是引用yayajiaojeff在2004-9-1 11:03:00的发言：

求通法的话则horsefish's answer is perfect. But if you want to find another way, 用代入法。

becuase the interest income is slightly above 80.00, then pick 8% first, semi-annual compound. You will find the interest income will be 81.6, $1.04 higher than 80.56. So the choice must be just slighthly lower than 8%. So choose C.

这个方法很管用呀!不过我想请问一下,如果直接算要怎么算呢?谢谢!