Q13:c／ｅ

Is the number of seconds required to travel d1 feet at r1 feet per second greater than the number of seconds required to travel d2 feet at r2 feet per second?

(1) d1 is 30 greater than d2.

(2) r1 is 30 greater than r2.

I think C is right. Is d1/r1 greater than

d2/r2?

d1/r1-d2/r2=(d1*r2-d2*r1)/(r1*r2)

if together with term 1 and 2,

d1=1.3d2 and r1=1.3r2 ,

so (d1*r2-d2*r1)/(r1*r2)=(1.3d2*r2-d2*1.3r2)/(r1*r2)=0

therefore, the time is the same.

in other words, it suffiently answer the question.

Am I right?

如果把这里改成30%greater，d1/r1和d2/r2比较大小。两者相除，商和1比较

大小，因为这里都是正数。d1=130%d2 r1=130r2，把d1/r1换成d1 r2的表达式

，一比，刚好等于1，就可以出结果啊？

我也犯了一样的错误，但是想确认一下这个思路本身又没有问题.

谢谢楼上两位！！