请教大牛

一战 · 发表于 2006-8-20 14:24:00

哪位大牛帮忙详解一下好吗？看不懂啊！

26) for savings into bank, for first 0 - 20,000, interest rate is 2 %, next 20,000 to 50,000 interest rate is 2.5%,and above 50,000 interest is 3.5%, what is the saving amount that the interest equal to 3%?

一战 · 发表于 2006-8-20 16:22:00

17.店里卖两种报，报A每份１元和报B每份1.25元，今天只卖了这两种报，r percent指的是报A收入占总收入的百分比，p percent指的是报A copies占总数的百分比，问r怎么用p来表示.

r=400p/(500-p) 注意这里是百分比

设
报a的数量是 x，b的数量是y

a*x/(a*x+y*b)=r%; x/(x+y)=p%;消去x，y得请教高人此处是如何消去X，Y的？？？

r=400p/(500-p) 注意这里是r，p百分比

gonghao · 发表于 2006-8-20 17:57:00

17题

x/(x+y)=p%

解出y

代入a*x/(a*x+y*b)=r%

就ok了，X可以在计算时约去

gmaht · 发表于 2006-8-20 18:16:00

assume y dollars will give you an overall 3%:

first 20000 x 2% = 400
next (20000-50000): 30000 x 2.5% = 750
above 50000 : (y-50000)x3.5% = 3.5%y-1750

then the overall interest rate:

[ 400+750+3.5%y-1750 ] / y = 3%
===> y=120000

一战 · 发表于 2006-8-21 02:46:00

多谢好心的XDJM指点了！！！

请教大牛

请教大牛

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