A boat traveled upstream adistance of 90 miles at an average speed of (v - 3) miles per hour and thentraveled the same distance downstream at an average speed of (v + 3) miles perhour. If the trip upstream took half anhour longer than the trip downstream, how many hours did it take the boat totravel downstream?
2.5
2.4
2.3
2.2
2.1
求的不是V!!!是how many hours did it take the boat to travel downstream
是 90/(V+3)
90=r(t+0.5)=(r+6)t 得出r=12t。把r=12t 代入上式,得:
2t^2+t-15=0 解得t1=2.5,t2=-3。