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
We can PLUG IN THE ANSWERS, which represent the number of hours that the boat took to travel downstream.
When the correct answer choice is plugged in, the time upstream will be 1/2 hour longer than the time downstream.
The most likely answer choice is
A -- the only option that divides evenly into 90.
Answer choice A: 2.5 hours to travel downstream.
Rate downstream = d/t = 90/(2.5) = 36 miles per hour.
Thus, v+3 = 36, implying that v=33.
Rate upstream = v-3 = 33-3 = 30 miles per hour.
Time upstream = d/r = 90/30 = 3 hours.
Time upstream - time downstream = 3-2.5 = .5.
Success!
The correct answer is
A.
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