SOLUTION: the speed of a river's current is 4mph. a boat travels 40 miles upstream at a constant rate of speed. if the speed has been 9mph faster, the trip would have taken 1 hour less time.
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Question 803654: the speed of a river's current is 4mph. a boat travels 40 miles upstream at a constant rate of speed. if the speed has been 9mph faster, the trip would have taken 1 hour less time. what is the boat's speed in still water?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
the speed of a river's current is 4mph. a boat travels 40 miles upstream at a constant rate of speed. if the speed has been 9mph faster, the trip would have taken 1 hour less time. what is the boat's speed in still water?
current speed = 4 mph
boat speed in still water =x
upstream speed = x-4
t=d/r
40/(x-4) hours
--
If spee}}}d was increased by 9 mph
speed = (x-4+9) = x+5
t= 40/(x+5)
difference in time = 1 hour
40(x+5)-40(x-4) =(x-4)(x+5)*1
40x+200-40x+160=x^2+x-20
x^2+x-380=0
x^2+20x-19x-380=0
x(x+20)-19(x+20)=0
(x+20)(x-19)=0
x=-20 OR 19
ignore negative
speed in still water = 19mph
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