[問題]GWD30-27

[racherlin]

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.

答案是B

麻煩各位幫忙解答 謝謝

[cssteph]

(1)不知道r是多少也不知道到底工作幾小時 =>不充分
(2)2.4r - r = 1.4r (至少工作4個小時)
1.4r/0.2r=7
所以總共工作4+7=11小時

我是這樣想的，不知道對不對嚕^^"