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Question 73072: If a boat goes downstream 72 miles in 3 hours and upstream 60 miles in 6 hours, the rate of the river and the rate of the boat in still water respectively are?
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website! If a boat goes downstream 72 miles in 3 hours and upstream 60 miles in 6 hours, the rate of the river and the rate of the boat in still water respectively are?
:
Let s = speed of the boat, & c = current
Speed upstream = (s-c)
Speed downstream = (s+c)
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Two unknowns, two distance equation, Dist = time * speed
:
3(s + c) = 72
Simplify divide equation by 3:
s + c = 24
And:
6(s - c) = 60
Simplify divide equation by 6
s - c = 10
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Use the elimination method on these two simplified equations
s + c = 24
s - c = 10
----------------adding eliminates c
2s = 34
s = 34/2
s = 17 mph boat speed
:
Find the current:
s + c = 24
17 + c = 24
c = 24 - 17
c = 7 mph is the current.
:
;
Check our solutions in: 3(s + c)= 72 and 6(s-c) = 60
3(24) = 72
and
6(10) = 60
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