Answer:
The streamer's speed in still water is 90.23 km/h while the stream's speed is 33.33 km/h
Explanation:
Let v = streamer's speed in still water and v' = stream's speed. His speed upstream is V = v + v' and his speed downstream is V' = v - v'.
Since he travels 36 km upstream, the time taken is t = 36/V = 36/(v + v').
he travels 32 km downstream, the time taken is t' = 32/V' = 32/(v - v')
The total time is thus t + t' = 36/(v + v') + 32/(v - v')
Since the whole trip takes 6,5 hours,
36/(v + v') + 32/(v - v') = 6.5 (1)
Multiplying each term by (v + v')(v - v'), we have
(v + v')(v - v')36/(v + v') + (v + v')(v - v')32/(v - v') = 6.5(v + v')(v - v') (1)
(v - v')36 + (v + v')32 = 6.5(v + v')(v - v') (1)
36v - 36v' + 32v + 32v' = 6.5(v² + v'²)
68v - 4v' = 6.5(v² + v'²) (2)
Also he travels 4 km upstream, the time taken is t" = 4/V = 4/(v + v').
he travels 40 km downstream, the time taken is t'" = 40/V' = 40/(v - v')
The total time is thus t" + t'" = 4/(v + v') + 40/(v - v')
Since the whole trip takes 180 minutes = 3 hours,
4/(v + v') + 40/(v - v') = 3 (3)
Multiplying each term by (v + v')(v - v'), we have
(v + v')(v - v')4/(v + v') + (v + v')(v - v')40/(v - v') = 3(v + v')(v - v') (1)
(v - v')4 + (v + v')40 = 3(v + v')(v - v') (1)
4v - 4v' + 40v + 40v' = 3(v² + v'²)
44v - 36v' = 3(v² + v'²) (4)
Dividing (2) by (4), we have
(68v - 4v')/(44v - 36v') = 6.5(v² + v'²)/3(v² + v'²)
(68v - 4v')/(44v - 36v') = 6.5/3
3(68v - 4v') = 6.5(44v - 36v')
204v - 12v' = 286v - 234v'
204v - 286v = 12v' - 234v'
-82v = -222v'
v = -222v'/82
v = 111v'/41
Substituting v into (2), we have
68v - 4v' = 6.5(v² + v'²)
68(111v'/41) - 4v' = 6.5[(111v'/41)² + v'²]
[68(111/41) - 4]v' = 6.5[(111/41)² + 1]v'²
[68(111/41) - 4]v' = 6.5[(111/41)² + 1]v'²
[7548/41 - 4]v' = 6.5[12321/1681 + 1]v'²
[(7548 - 164)/41]v' = 6.5[(12321 + 1681)/1681]v'²
[7384/41]v' = 6.5[14002/1681]v'²
[7384/41]v' = [91013/1681]v'²
[91013/1681]v'² - [7384/41]v' = 0
([91013/1681]v' - [7384/41])v' = 0
⇒ v' = 0 or ([91013/1681]v' - 7384/41) = 0
⇒ v' = 0 or [91013/1681]v' - 7384/41) = 0
⇒ v' = 0 or v' = 7384/41 × 16841/91013
⇒ v' = 0 or v' = 180.097 × 0.185
⇒ v' = 0 or v' = 33.33 km/h
Since v' ≠ 0, v' = 33.33 km/h
Substituting v' into v = 111v'/41 = 111(33.33 km/h)/41 = 3699.63 km/h ÷ 41 = 90.23 km/h
So, the streamer's speed in still water is 90.23 km/h while the stream's speed is 33.33 km/h