GMATprep一道数学题求助

If it took Carol 1/2 hour to cycle from his house to the library yesterday, was the distance that he cycled greater then 6 miles? ( 1mile=5,280feet)

1)      The average speed at which Carlos cycled from his house to the library yesterday was greater than 16 feet per second.

2)      The average speed at which Carlos cycled from his house to the library yesterday was less than 18 feet per second

答案是E

条件1：V=16feet/second=16/5280比1/3600=10.9mile/hour

       (脸红ing, 总是不会做单位换算，大家看我这么算对不？可是考试的时候算这些数字很烦的阿，有米有什么更简单的方法？)

条件2：V=18feel/second=18/5280比1/3600=12.27mile/hour

是不是因为条件1和2联立，得出S大于5.45小于6.14，所以不能得出是否大于6呢？谢谢

16feet/second

因为5280feet=1mile，所以16feet就是16/5280mile，1s=1/3600h，可以那么算的就是麻烦。最好用乘法都换成feet.

0.5hour=1800s. 16f/s*1800=28800feet.

6mile=31600feet，比那个好算一点。

条件2也一样。联立也不行。楼主解的很对啊……