SOLUTION: A boat moves 28 km/h in still water. It travels 80 km upstream and 80 km downstream in a total time of 7 hours. What is the speed of the current?

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Question 668812: A boat moves 28 km/h in still water. It travels 80 km upstream and 80 km downstream in a total time of 7 hours. What is the speed of the current?
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
Boat speed = 28 mph
current speed = x mph

against current = 28 - x
with current = 28 + x

Total distance = 80 miles Total Time= 7.00 hours
Time upstream + time downstream =

80/(28-x)+80/(28+x)= 7
80(28+x )+80(28 -x)=7(784-X^2)
2240+80 x+2240 -80x=5488-7X^2
4480 - -5488 = -7 X^2
-1008 = -7 X^2
-7 X^2= -1008
x^2 = 144
x = +/- 12

Speed of current = 12 km/h