蓝皮书37题

37. A bus trip of 450 miles would have taken 1 hour less if the average speed S for the trip had been greater by 5 miles per hour. What was the average speed S, in miles per hour, for the trip?

A.10

B.40

C.45

D.50

E55

正确答案是C。但不懂是怎样算出来的。

450/(s+5)=450/S  -  1

s=45