<PRE><B>Question 668812</B>
Boat  	speed	=	28	mph													
current     	speed	=	x	mph													
																	
against 	current	=	28	-	x												
with 	current	=	28	+	x 												
																	
Total distance =		80	miles 		Total Time=	7.00	hours  										
Time upstream + time downstream =																	
																	
80/(28-x)+80/(28+x)=	7					
80(28+x	)+80(28	-x)=7(784-X^2)
2240+80	x+2240	-80x=5488-7X^2					
4480	-	-5488	=			-7	X^2										
-1008	=		-7	X^2													
-7	X^2=	-1008															
x^2	=	144															
x =	+/-	12															
																	
Speed of current = 12 km/h									
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