Question 551669
Boat speed	=	40	km/h
current speed 	=	x	km/h
wind speed			
speed against	current	40	-x
speed with	current	40	+x
			
Distance against	current	x       	km
Distance with 	current	x        	km

time with current = 2 hours
y/(40+x) =2
y=2(40+x)
y=80+2x..........(1)

Time against current = 2 1/2 hours
y/(40-x)=5/2
y= 5(40-x)/2............(2)

equate equation (1) & (2)
80+2x=5(40-x)/2
multiply by 2
160+4x=200-5x
9x=40
/9
x=40/9

x=4.44 km/h speed of current

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