SOLUTION: A motorboat takes 5 hours to travel 100 km going upstream. The return trip takes 2 hours going downstream. What is the rate of the boat in still water and what is the rate of the c

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Question 1130823: A motorboat takes 5 hours to travel 100 km going upstream. The return trip takes 2 hours going downstream. What is the rate of the boat in still water and what is the rate of the current?
Rate of the boat in still water:
Rate of the current:

Found 2 solutions by josmiceli, MathTherapy:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
let s+ = the speed of the boat in still water in km/hr
Let +w+ = the speed of the current in km/hr
Going upstream:
(1) +100+=+%28+s+-+w+%29%2A5+
Going downstream:
(2) +100+=+%28+s+%2B+w+%29%2A2+
-------------------------------
(1) +5s+-+5w+=+100+
(2) +2s+%2B+2w+=+100+
Multiply (1) by 2+, multiply
(2) by +5+, and add the equations
-----------------------------------------------
(2) +10s+%2B+10w+=+500+
(1) +10s+-+10w+=+200+
-------------------------------
+20s+=+700+
+s+=+35+
and
(2) +2%2A35+%2B+2%2Aw+=+100+
(2) +2w+=+30+
(2) +w+=+15+
-----------------------------
Rate in still water: 35 km/hr
Rate of the current: 15 km/hr

Answer by MathTherapy(10555) About Me  (Show Source):
You can put this solution on YOUR website!

A motorboat takes 5 hours to travel 100 km going upstream. The return trip takes 2 hours going downstream. What is the rate of the boat in still water and what is the rate of the current?
Rate of the boat in still water:
Rate of the current:
Let boat speed, in still water, be S, and speed of current, C
Then we get the following system of equations for the 2 speeds:
2S = 70 ------- Adding eqs (ii) & (i)
Speed of boat, or highlight_green%28matrix%281%2C6%2C+S%2C+%22=%22%2C+70%2F2%2C+%22=%22%2C+35%2C+mph%29%29
Speed of current, or highlight_green%28matrix%281%2C6%2C+C%2C+%22=%22%2C+50+-+35%2C+%22=%22%2C+15%2C+mph%29%29