求解一题DS！！

yolanda1204

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

我认为选C ，可是答案是E

yuntianlau

答案是E

d1/r1-d2/r2=(d2+30/r2+30)-d2/r2=30(r2-d2)/r2(r2+30)

无法确定r2与d2谁大 所以不能确定

yolanda1204

谢谢你!!!