Question 123077
Onward journey along the stream:
speed=x+2
time=10min=10/60=1/6 hour
distance=speed*time=(1/6)*(x+2)

return Journey against stream:
speed=x-2
time=30min=30/60=1/2 hour
distance=speed*time=(1/2)*(x+2)

Equating both distances

we get 
(1/6)*(x+2)=(1/2)*(x+2)
multiply throughout by 6,
x+2=3(x-2)
x+2=3x-6
interchange sides
3x-6=x+2
3x-x=2+6
2x=8
x=4
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Speed onward=x+2=6mph
time=1/6
Distance=6*1/6=1 mile
The answer = 1 mile
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Verification
Return speed=x-2=4-2=2 mph
Time=1/2 hour
Distance=2*(1/2)=1 mile
okay