SOLUTION: Bryan's boat travels 15 km/h in still water.He motors 140 km downstream in the same time it takes to travel 35 km upstream. What is the speed of the river?

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Question 909912: Bryan's boat travels 15 km/h in still water.He motors 140 km downstream in the same time it takes to travel 35 km upstream. What is the speed of the river?
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
r*t=d
(15-c)*t=35
15*t-c*t=35
(15+c)*t=140
15*t-c*t=35
15*t+c*t=140
add
30t=175
t=175/30
t=5.83333333 5 hr 50 minutes hr
15*5.83333333+c*5.83333333=140
87.5+c*5.83333333=140
c*5.83333333=52.5
c=52.5/5.83333333
c=9.0 mph current
check
(15+c)*t=140
(15+9)*5.83333333=140
(24)*5.83333333=140
140.0=140
(15-c)*t=35
(15-9)*5.83333333=35
(6)*5.83333333=35
35.0=35
ok