Answer:
boat traveled downstream a distance of 45 mi ad then came right back. if the speed of the stream was 12 mph and the total trip took 5 hours, find the average speed of the boat relative to the water
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let x= speed of boat in still water
x+12= speed of boat in downstream
x-12= speed of boat in upstream
..
travel time=distance/speed
45/(x+12)+45/(x-12)=5
45(x-12)+45(x+12)=5(x+12)(x-12)
45(x-12+x+12)=5(x^2-144)
90x=5x^2-720
5x^2-90x-720=0
x^2-18x-144=0
(x+6)(x-24)=0
x=-6 (reject, x>0)
x=24
average speed of the boat relative to the water: speed of boat twice the speed of the water
