SOLUTION: A motorboat makes a round trip on a river 56 miles upstream and 56 miles downstream, maintaining the constant speed of 15 mph relative to the water. The entire trip up and back tak
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Question 656081: A motorboat makes a round trip on a river 56 miles upstream and 56 miles downstream, maintaining the constant speed of 15 mph relative to the water. The entire trip up and back takes 7.5 hours. What is the speed of the current? Answer by lwsshak3(11628) (Show Source):
You can put this solution on YOUR website! A motorboat makes a round trip on a river 56 miles upstream and 56 miles downstream, maintaining the constant speed of 15 mph relative to the water. The entire trip up and back takes 7.5 hours. What is the speed of the current?
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let x=speed of current
speed of boat downstream=15+x (relative to land)
speed of boat upstream=15-x (relative to land)
Travel time=distance/speed
..
56/(15+x)+56/(15-x)=7.5
LCD:(15+x)(15-x)
56(15-x)+56(15+x)=7.5(15+x)(15-x)
840-56x+840+56x=7.5(15^2-x^2)
1680=7.5(225-x^2)
divide both sides by 7.5
224=225-x^2
x^2=1
x=1
speed of current=1 mph
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