Respuesta :
Answer:9/2 km per hour
Step-by-step explanation:
equation,
6/9-x + 6/x=8/3
Upstream is flowing of the boat in the opposite direction of the stream. The speed of the river current is 4.5 km per hour.
Given-
Johnny and his father go fishing at 5:00 AM.
Total traveled by the Johnny and his father in upstream is 6 km.
The speed of the boat is 9 km/h.
What is upstream?
Upstream is flowing of the boat in the opposite direction of the stream.
Let x be the speed of the river current.
Time taken by the Johnny and his father to travel 6 km in upstream is ,
[tex]=\dfrac{6}{9-x}[/tex]
The time taken by the bottle to floats in the current river is,
[tex]=\dfrac{6}{x}[/tex]
As Johnny and his father start from 5:00 AM and the bottle reached to the point where Johnny and his father began their trip at 7:40 AM. Thus the total time is,
[tex]=7:40-5:00[/tex]
[tex]=2:40[/tex]
In hours,
[tex]=2\dfrac{40}{60}[/tex]
[tex]=\dfrac{8}{3}[/tex]
As the total time is equal to the sum of the Time taken by the Johnny and his father to travel 6 km in upstream and The time taken by the bottle to floats in the current river. Thus,
[tex]\dfrac{6}{9-x}+\dfrac{6}{x}=\dfrac{8}{3}[/tex]
[tex]\dfrac{6x+54-6x}{9x-x^2}= \dfrac{8}{3}[/tex]
[tex]\dfrac{27}{9x-x^2}= \dfrac{4}{3}[/tex]
[tex]x^2-9x+\dfrac{81}{4}=0[/tex]
On solving the above quadratic equation we get the positive value of the x is 4.5.
Thus the speed of the river current is 4.5 km per hour.
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