Question 813725
still water 9 mph
current - x mph

down stream = 9+x
upstream = 9-x

time upstream - time downstream = 5 hours

t=d/r

55/(9-x) -55/(9+x)=5

55(9+x)-55(9-x)=5(9^2-x^2)

495+55x-495+55x=405-5x^2

5x^2+110x-405=0

Find the roots of the equation by quadratic formula							
							
a=	5	,	b=	110	,	c=	-405
							
b^2-4ac=	12100	+	8100				
b^2-4ac=	20200						
{{{	sqrt(	20200	)=	142.13	}}}		
{{{x=(-b+-sqrt(b^2-4ac))/(2a)}}}							
{{{x1=(-b+sqrt(b^2-4ac))/(2a)}}}							
x1=(	-110	+	142.13	)/	10		
x1=	3.21						
{{{x2=(-b-sqrt(b^2-4ac))/(2a)}}}							
x2=(	-110	-142.13	) /	10			
x2=	-25.21						
Ignore negative value							
current   	speed	3.2	mph