GWD30 -27 请问大家都选什么呢？

christdj · 发表于 2011-7-19 03:04:29

Q27:
For each landscaping job that takes more than 4 hours, a certain contractor charges a total of r dollars for the first 4 hours plus 0.2r dollars for each additional hour or fraction of an hour, where r > 100. Did a particular landscaping job take more than 10 hours?
(1) The contractor charged a total of $288 for the job.
(2) The contractor charged a total of 2.4r dollars for the job.

大概没领悟精髓~选D还是B呢......

小sai爱mj · 发表于 2011-7-19 09:30:56

觉得1是推不出来的。因为r没有给上限，所以r取101和r取200的时候，1选项的答案是不同的。

bitieming · 发表于 2011-7-19 11:30:06

选B，条件1列式r+0.2rt=288，t取值在6上下都可以解出r的响应解，因此无法判断。

christdj · 发表于 2011-7-19 14:43:14

明白啦~谢谢！

GWD30 -27 请问大家都选什么呢？

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