07prep-ps1第153题

153.A boat traveled upstream a distance of 90 miles at an average speed of (v - 3) miles per hour and then traveled the same distance downstream at an average speed of (v + 3) miles per hour.  If the trip upstream took half an hour longer than the trip downstream, how many hours did it take the boat to travel downstream?

(A) 2.5

(B) 2.4

(C) 2.3

(D) 2.2

(E) 2.1

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