SOLUTION: Jared & his boy are boating the Green River in Ky. It takes them 4 hrs. to travel 56 mi. downstream. On the same return trip, it takes them 7 hrs. How fast is the boat in still wat

Question 816540: Jared & his boy are boating the Green River in Ky. It takes them 4 hrs. to travel 56 mi. downstream. On the same return trip, it takes them 7 hrs. How fast is the boat in still water? How fast is the current?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
boat speed =x mph
current speed =y mph
against current 7 hours
with current 4 hours

Distance against 56 miles distance with 56 miles
t=d/r against current -
56.00 / ( x - y )= 7.00
7.00 ( x - y ) = 4.00
7.00 x - 7.00 y = 56.00 ....................1

56.00 / ( x + y )= 4.00
4.00 ( x + y ) = 56.00
4.00 x + 4.00 y = 56.00 ...............2
Multiply (1) by 4.00
Multiply (2) by 7.00
we get
28.00 x + -28.00 y = 224.00
28.00 x + 28.00 y = 392.00
56.00 x = 616.00
/ 56.00
x = 11.00 mph

plug value of x in (1) y
7.00 x -7.00 y = 56.00
77.00 -7.00 -77.00 = 56.00
-7.00 y = 56.00
-7.00 y = -21.00 mph
y = 3.00
boat speed 11.00 mph
current speed 3.00 mph

m.ananth@hotmail.ca

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