SOLUTION: a boat goes 7 mph in still water. It takes as long to go 20 mi upstream AS 50 mi downstream. Find the rate of the current.

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Question 914016: a boat goes 7 mph in still water. It takes as long to go 20 mi upstream AS 50 mi downstream. Find the rate of the current.
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
Boat speed = 7 km/h
current speed = x km/h

speed against current 7 - x
speed with current 7 + x

Distance against current 20 miles
Distance with current 50 miles

t=d/r time against = time with current -
20 / ( 7 - x )= 50 / ( 7 + x )
20 ( 7 + x )= 50 ( 7 -x )
140 + 20 x = 350 - -50 x
50 x 20 x 350 + -140
70 x = 210
/ 70
x = 3 km/h current speed