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

(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

我用的办法比较死啦

就是求在第二象限的那条线与X轴角度,然后知道要求的那个点在的线与X的角度,知道半径,就可以知道那个点的坐标了