SOLUTION: A boat travelled 210 miles downstream and back. The trip downstream took 10 hours. the trip back took 70 hours. What is the speed of the boat in still water? What is the speed
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Question 509113: A boat travelled 210 miles downstream and back. The trip downstream took 10 hours. the trip back took 70 hours. What is the speed of the boat in still water? What is the speed of the current?
I tried several things, none of them worked. I've turned this problem every which way and still can't find the solution.
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
Boat speed =x mph
current speed =y mph
against current x-y 70.00 hours
With current x+y 10.00 hours
Distance = same= 210 miles
t=d/r
210 / ( x - y )= 70.00
70 ( x - y ) = 210.00
70 x -70 y = 210 ....................1
210 / ( x + y )= 10.00
10.00 ( x + y ) = 210
10.00 x + 10.00 y = 210 ...............2
Multiply (1) by 1.00
Multiply (2) by 7.00
we get
70 x + -70 y = 210
70 x + 70 y = 1470
140 x = 1680
/ 140
x = 12 mph
plug value of x in (1)
70 x -70 y = 210
840 -70 y = 210
-70 y = 210 -840
-70 y = -630
y = 9 mph
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