GWD-30-27涛涛 求解

赵小团

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.
    
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.


Answer: B
不明白怎么求出来的....

kazemi

假设共工作x小时，
（1）的话x=1440/r-1，where r>100，但在r>131之后，x就小于10了，所以不够充分
（2）的话可以直接算出x=11