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标题: 问一道PREP 5 题目 [打印本页]

作者: GMAT760!! 时间: 2019-9-12 06:22
标题: 问一道PREP 5 题目
How much more interest will Maria receive if she invests $1,000 for one year at x percent annual interest, compounded semiannually, than if she invests $1,000 for one year at x percent annual interest, compounded annually?

答案是x^2/40
大家知道是怎么做的吗

作者: GMAT760!! 时间: 2019-9-12 07:05
Last month a phone company charged $0.07 per minute for the first 300 minutes of calling time and $0.05 per minute for each minute of calling time in excess of the first 300 minutes. For how many minutes of calling time was Bob charged by the phone company last month?

(1) Last month the phone company charged Bob $21.00 for his calling time that was charged at the rate of $0.07 per minute.
(2) Last month the phone company charged Bob $40.00 for his calling time that was charged at the rate of $0.05 per minute.
还有这道为什么（1）是不对的啊

作者: ltsg 时间: 2019-9-12 10:46
1000[1+1/2(x/100)]^2-1000(1+x/100) 半年复利要按半年的利率算

(1)只能说明Bob打电话的时间不低于300minutes

作者: GMAT760!! 时间: 2019-9-12 11:05

ltsg 发表于 2019-9-12 10:46
1000[1+1/2(x/100)]^2-1000(1+x/100) 半年复利要按半年的利率算

(1)只能说明Bob打电话的时间不低于300mi ...

但是第二问难道说的不是公司收取来Bob21 块钱，0.07 因此我们可以算出300. 然后 300 不是Bob打电话的费用吗

作者: wyc0930 时间: 2019-9-12 12:00
注意是x percent 即x%
1000*（1+x%/2）^2-1000*（1+x%）= 1000*（x^2/40000）=x^2/40

作者: wyc0930 时间: 2019-9-12 12:03

GMAT760!! 发表于 2019-9-12 11:05
但是第二问难道说的不是公司收取来Bob21 块钱，0.07 因此我们可以算出300. 然后 300 不是Bob打电话的费 ...

条件1情况下 300分钟和301分钟 302 分钟等等都符合不能确定到底打了几分钟电话

作者: GMAT760!! 时间: 2019-9-12 12:19

wyc0930 发表于 2019-9-12 12:00
注意是x percent 即x%
1000*（1+x%/2）^2-1000*（1+x%）= 1000*（x^2/40000）=x^2/40

thanks 我懂了

作者: GMAT760!! 时间: 2019-9-12 12:21

wyc0930 发表于 2019-9-12 12:03
条件1情况下 300分钟和301分钟 302 分钟等等都符合不能确定到底打了几分钟电话 ...

好的吧，我以为在所有的情况下是收了0.7percent的，我懂了谢谢

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