a person rowing at the rate of 5 km/h in still water , takes thrice as much as time in going 40km upstream as in going 40 km downstream . find the speed of the stream. faster frnd itsss really important.
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then
(5+x) = boat speed downstream
and
(5-x) = boat speed upstream
;
Let d = distance one way
;
write a time equation; Time = distance /speed:
upstream time = 3 times downstream time
d/5-x = d/3(5-x)
d/5-x = 3d/(5-x)
Cross multiply
d(5+x) = 3d(5-x)
:
divide both sides d and eliminate it:
5 + x = 3(5 - x)
;
5 + x = 15 - 3x
:
x + 3x = 15 - 5
:
4x = 1
x = 10/4
x = 2.5 km/hr is the rate of the current
:
:
Check solution by finding the distances, should be equal:
5 + 2.5 = 7.5
3(5 - 2.5) = 7.5