SOLUTION: A motorboat can travel upstream on a river at 18 km/h and downstream at 30 km/h. How far upstream can the boat travel if it leaves at 8:00 AM and must return by noon?

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Question 398821: A motorboat can travel upstream on a river at 18 km/h and downstream at 30 km/h. How far upstream can the boat travel if it leaves at 8:00 AM and must return by noon?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The round trip from 8 - noon is 4 hours
Let t = time for upstream trip
Then 4+-+t = time for downstream trip
Going upstream:
d+=+18t
Going downstream:
d+=+30%2A%284+-+t%29
Then,
18t+=+120+-+30t
48t+=+120
t+=+2.5
So, going upstream:
d+=+18%2A2.5
d+=+45
He travels 45 mi upstream