[問題]GWD19-10

[sonnia]

Q10:
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

為何答案是d呢？？？

我自己是選a
而且1.08的平方 就1.16 超過了1.15
那這樣子r就不法確定是否超過8啦
那為啥答案是D呢???

SORRY 大概是因為第一次寫GWD 所以問題一堆...
抱歉><"

[Ace]

題目轉錄錯誤
應為(1 + r/100)^n

條件二
(1 + r/100)^2 > 1.15
我用excel算了一下
(1 + r/100)> 1.072
在題目沒有說r必為整數的假設下
條件二不充分....

我認為應選A

[sonnia]

SORRY 沒注意到題目錯誤

謝謝您幫我改正 謝謝～～

那這麼說 答案應該是A囉～

謝謝

[chris8888]

(1)The deposit earns a total of $210 in interest in the first 2 years.
210 = 1000{(1+r/100)^2 - 1}
1210 = 1000{(1+r/100)^2}
121/100 = {(1+r/100)^2}
(11/10)^2 = (1+r/100)^2
(1 + 10/100)^2 = (1 + r/100)^2 <== 求得 r = 10. r > 8 成立

(2)(1 + r/100)2 > 1.15
1.07 * 1.07 = 1.1449, 但1.08 * 1.08 = 1.1664 已經超過, 因此insufficient

更正, 答案是A