SOLUTION: a speed boat takes 3 hours longer to go 45 miles up a river than to return. if the boat cruises at 20 mph in still water, what is the rate of the current
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Question 887905: a speed boat takes 3 hours longer to go 45 miles up a river than to return. if the boat cruises at 20 mph in still water, what is the rate of the current Answer by lwsshak3(11628) (Show Source):
You can put this solution on YOUR website! a speed boat takes 3 hours longer to go 45 miles up a river than to return. if the boat cruises at 20 mph in still water, what is the rate of the current
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let c=rate of current
20+c=speed of boat down river
20-c=speed of boat up river
travel time=distance/speed
lcd: (20+c)(20-c)
900+45c-900+45c=3(20^2-c^2)=3(400-c^2)=1200-3c^2
90c=1200-3c^2
3c^2+90c-1200=0
c^2+30c-400=0
(c+40)(c-10)=0
c=-40 reject
or
c=10
rate of the current=10 mph
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