SOLUTION: it takes about 1 1/2 hours to go 12 km downstream and 6 hours to return. Find the speed of the boat in still water and the speed of the current.

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Question 768080: it takes about 1 1/2 hours to go 12 km downstream and 6 hours to return. Find the speed of the boat in still water and the speed of the current.
Answer by mananth(16946) (Show Source):
You can put this solution on YOUR website!
Boat speed speed =x kph
current speed =y kph
against current 6 hours
with current 1.5 hours

Distance against 12 miles distance with 12 miles
t=d/r against current -
12 / ( x - y )= 6
6 ( x - y ) = 12
6 x - 6 y = 12 ....................1

12 / ( x + y )= 1.50
1.50 ( x + y ) = 12
1.50 x + 1.50 y = 12 ...............2
Multiply (1) by 1
Multiply (2) by 4
we get
6.00 x + -6 y = 12
6.00 x + 6 y = 48
12 x = 60
/ 12
x = 5 kph

plug value of x in (1)
6 x -6 y = 12
30 -6 y = 12
-6 y = 12 -30
-6 y = -18 mph
y = 3
Boat speed speed 5 kph
current speed 3 kph

m.ananth@hotmail.ca