SOLUTION: A fisherman can row a boat 8km downstream and return in 100min. If the speed of the stream is 2km per hour, find the speed of the boat in still water?

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Question 696790: A fisherman can row a boat 8km downstream and return in 100min. If the speed of the stream is 2km per hour, find the speed of the boat in still water?
Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
A fisherman can row a boat 8km downstream and return in 100min. If the speed of the stream is 2km per hour, find the speed of the boat in still water?
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let x=speed of boat in still water
x+2=downstream speed
x-2=upstream speed
speed=distance/travel time
8/(x+2)+8/(x-2)=100/60
LCD:(x+2)(x-2)
8(x-2)+8(x+2)=(100/60)*(x+2)(x-2)
8(x-2+x+2)=100(x+2)(x-2)/60
240(2x)=100(x^2-4)
480x=100x^2-400
100x^2-480x-400=0
10x^2-48x-40=0
solve by following quadratic formula:
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
a=10, b=-48,c=-40
ans: x≈5.52
speed of boat in still water≈5.52 km/hr