SOLUTION: A fishing boat took 3h to travel 36 km upstream, against the current, on the st Lawrence river. The same trip downstream only took 2h. What is the average speed of the fishing b

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: A fishing boat took 3h to travel 36 km upstream, against the current, on the st Lawrence river. The same trip downstream only took 2h. What is the average speed of the fishing b      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


    

Question 715782: A fishing boat took 3h to travel 36 km upstream, against the current, on the st Lawrence river.
The same trip downstream only took 2h.
What is the average speed of the fishing boat in still water? What was the speed of the over current ?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +c+ = the speed of the current in km/hr
Let +b+ = the speed of the boat in still water in km/hr
+b+-+c+ = the speed going upstream in km/hr
+b+%2B+c+ = the speed going downstream in km/hr
----------------
Going upstream:
(1) +36+=+%28+b+-+c+%29%2A3+
Going downstream:
(2) +36+=+%28+b+%2B+c+%29%2A2+
---------------------
(1) +b+-+c+=+12+
(2) +b+%2B+c+=+18+
Add the equations
+2b+=+30+
+b+=+15+
Plug this result back into (1) or (2)
(2) +15+%2B+c+=+18+
(2) +c+=+3+
The speed of the boat in still water was 15 mk/hr
The speed of the current was 3 km/hr