GWD19一道数学题

chenmorning

If $1,000 will be deposited in a bank account and I is the dollar amount of interest earned from the original deposit, represented as I = 1000 {(1 + r/100)ⁿ – 1}, and the annual interest rate is r percent, is r > 8 percent?

(1) The deposit earns a total of $210 in interest in the first 2 years.

(2) (1 + r/100)² > 1.15

我觉得应该是A，但是答案给出是D，请大家讨论，谢谢！

himba

我是这么想的饿。

条件(1)1000{(1+r/100)^2-1)}=210得出(1+r/100)^2=1.21

算出r/100=0.1,r=10% 可以得出r>8%

条件(2)把r=8%代入第二个条件,得出1.08^2<1.15,而条件中给出的

(1+r%)^2>1.15>(1+8%)^2

所以也可以得出r>8%.

所以选D.

不知道这样说有没有弄清楚?