Question 381454
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This is a multi stage problem
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Let walking rate be x mph
Rowing rate in still water = 1.2x ( 20% more)
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Let rate of current = y mph
Calculate time A---->B-------->C
Ato B (down stream)
time = 4/(1.2x+y)
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B to C  (walk)
time = 3/x 
Time A  to B  to C 
=4/(1.2x+y)+3/x 
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AC ^2 = AB^2 +BC^2
AC^2=4^2+3^2
AC^2=25
AC = 5 miles
Time to walk from A  to C = 5/x
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Time from A to B to C = Time from A to C (walking)
4/(1.2x+y) + 3/x = 5/x
4/(1.2x+y)= 5/x-3/x
4/(1.2x+y)= 2/x
cross multiply
4x=2(1.2x+y)
4x=2.4x+2y
4x-2.4x=2y
1.6x=2y
/2
0.8x= y speed of current
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TIME RETURN
3/x + 4/(1.2x-y)(upstream)
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Time return - time forward = 8/5 hours
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(3/x + 4/(1.2x-y))- (4/(1.2x+y) + 3/x)= 8/5
y=0.8x
plug value of y
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(3/x + 4/(1.2x-0.8x))- (4/(1.2x+0.8x) + 3/x)= 8/5
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(3/x +4/0.4x)-(4/2x+3/x)=8/5
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(3/x+10/x)-(2/x+3/x)=8/5
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(13/x)-(5/x)=8/5
8/x=8/5
x=5 mph rate of walk.
Rate of rowing in still water = 1.2x = 1.2 * 5 = 6 mph.
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Cheers
m.ananth@hotmail.ca