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Answers
Answer:
Step-by-step explanation:
Let the speed of the stream =x km/hr
Let the speed of the boat in still water =y km/hr
Upstream speed = (y − x) km/hr
Downstream speed = (y + x) km/hr
time = distance / speed
The boat goes 30 km downstream and 36 km upstream in 6 hours.
6 = 30 / (y + x) + 36 / (y - x)
If the boat goes 45 km downstream and 18 km upstream in 5 hours.
5 = 45 / (y + x) + 18 / (y - x)
Let 1 / (y + x) = u
and, 1 / (y - x) = v
30u + 36v = 6 --------------(i)
45u + 18v = 5 --------------(ii)
Multiply eq-ii with (2) and subtract eq-i and eq-ii
30u + 36v = 6------------------(iii)
-90u - 36v = 10------------------(iv)
From iii and iv we get
u = 1/15 and v = 1/9
As we assume that
1 / (y + x) = u
y + x = 1 / u
y + x = 15-----------(v)
1 / (y - x) = v
y - x = 1 / v
y - x = 9----------------------(vi)
BY SOLVING (v) and (vi) using elimination method,
We get,
y = 12 and x = 3
Therefore,
Speed of boat in stream = 3km/hr
Speed of boat in still water = 12km/hr
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Answer:
in sterm - 3km/hr
in water- 12 km/hr
is the correct answer