求PREP上一道应用题目

门萨来了

50.  4230-!-item-!-187;#058&003784

A construction company was paid a total of $500,000 for a construction project.  The company's only costs for the project were for labor and materials.  Was the company's profit for the project greater than $150,000 ?

 

(1)  The company's total cost was three times its cost for materials.

 

(2)     The company's profit was greater than its cost for labor.

--------------------------------------------------------------------------------------------------------------------------------------------------------

【答案】C

【思路】profit= total – (labor+ material)  問profit>150000

(1) (l+m)=3m    -------------------------------------------------------------------insufficient

(2)  p>l   ---------------------------------------------------------------------------- insufficient

(1)(2)p=500,000-(l+m), p=500000- (l+
                        l), P=500000-1.5l
            

數字代入法P=15(千), l=23(千) ; P=25(千),l=16(千)  -------------------------- sufficient

最后的这个解释:數字代入法P=15(千), l=23(千) ; P=25(千),l=16(千)  -------------------------- sufficient没有看明白

我是最后一步列的是这个式子

P=500,000-(L+1/2L)>L, L<233.3

题目中说P>L,但是P和233.3的关系不清楚啊,所以怎么能是C呢?

困惑了

请高人指教

门萨来了

以下是引用racheloving在2009-1-12 21:18:00的发言：

P=500,000-(L+1/2L)>L, L<233.3 这个除错了吧

l<200000

 p>500000-1.5*200000>200000

果然算错了，谢谢ＭＭ提醒

moon2060

设material cost 为m，则total cost为3m，labor cost是2m，profit为p

p=500000-3m

由条件二知道p>2m， 即m<p/2，则-3m>-3p/2,将这个不等式带入到上面的等式中，可以得到p>500000-3p/2

解不等式，得到p>200000