SOLUTION: Alvin paddled for 3 hours with a 5​-km/h current to reach a campsite. The return trip against the same current took 8 hours. Find the speed of the boat in still water.

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Question 1129054: Alvin paddled for 3 hours with a 5​-km/h current to reach a campsite. The return trip against the same current took 8 hours. Find the speed of the boat in still water.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = speed of boat in still water
+s+%2B+5+ = speed going with the current
+s+-+5+ = speed going against the current
Let +d+ = the one-way distance
----------------------------------------------------
Going with the current:
(1) +d+=+%28+s+%2B+5+%29%2A3+
Going against the current:
(2) +d+=+%28+s+-+5+%29%2A8+
--------------------------------
+%28+s+%2B+5+%29%2A3+=+%28+s+-+5+%29%2A8+
+3s+%2B+15+=+8s+-+40+
+5s+=+55+
+s+=+11+
The speed in still water is 11 km/hr
-------------------------------------------
check:
(1) +d+=+%28+11+%2B+5+%29%2A3+
(1) +d+=+48+ km
and
(2) +d+=+%28+11+-+5+%29%2A8+
(2) +d+=+48+ km
OK