Asked by pankaj khanna
A person going at a rate of 5 km/hr in still water,takes thrice as much time in going 40km upstream as in going downstream. Find the speed of the stream.
Answers
Answered by
Reiny
let the speed of the current be x km/h
time against the current = 40/(5-x)
time with the current = 40/(5+x)
40/(5-x) = 3(40)/(5+x)
1/(5-x) = 3(5+x)
15-3x = 5+x
-4x=-10
x=2.5
the speed of the stream is 2.5 km/h
check:
time against the current = 40/2.5 = 16 hrs
time withe the current = 40/7.5 = 5 1/3 hrs
3 times 5 1/3 hrs = 16 hrs
time against the current = 40/(5-x)
time with the current = 40/(5+x)
40/(5-x) = 3(40)/(5+x)
1/(5-x) = 3(5+x)
15-3x = 5+x
-4x=-10
x=2.5
the speed of the stream is 2.5 km/h
check:
time against the current = 40/2.5 = 16 hrs
time withe the current = 40/7.5 = 5 1/3 hrs
3 times 5 1/3 hrs = 16 hrs
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