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标题: 求救：新prep数学的154题装cableTV的 [打印本页]

作者: rruizhang 时间: 2010-5-2 12:46
标题: 求救：新prep数学的154题装cableTV的
To install cable television in a home, a certain cable company charges a basic fee of $30 plus a fee of $20 for each cable outlet installed in the home.How much did the cable company charge the Horace family for installing cable television in their home?

(1) The cable company installed three cable outlets in the Horace family home.

(2) The amount that the cable company charged the Horace family for installing cable television in their home was equivalent to an average (arithmetic mean) charge of $30 per cable outlet installed.

--------------------------------------------------------------------------------------------------------------------------------------------------------【答案】D

请讲讲第二个条件的意思，怎么也看不懂。我在网上搜到这样的解答：

Avg Cost = total cost / # of outlets

Let's call the number of outlets "n".

Total cost will therefore be $30 + $20(n)

So, we can write the formula as:

30 = (30 + 20n)/n
30n = 30 + 20n
30n - 20n = 30
10n = 30
n = 30/10 = 3
可是根据条件2怎么能推出30 = (30 + 20n)/n 呢？

作者: Queeny11 时间: 2010-5-2 16:35
30x=30+20x
x=3

一共安装要用的钱。和如果每个按照30刀算的价格是一样的。。

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