Question

the speed of a boat is still is 13km per hour if the boat travels 84.7km down stream in 5.5,hours find the speed of stream the answer is 2.4km please solve correct answer ​

Answer 1

Answer:

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Step-by-step explanation:

Let’s first consider the movement downstream. The distance covered is simply 30 km. Using [math]u[/math] as the speed of the stream, the downstream speed is [math]15 + u[/math] km/hr.

Using our equation, the time taken to travel downstream is:

[math]t_d = \frac {30}{15 + u}[/math]

Now, what about movement upstream? The distance covered is still 30 km, whereas the speed is [math]15 - u[/math]. So,

[math]t_u = \frac {30}{u - 15}[/math]

From the question, we are told that the total time of travel is 4.5 hours, so:

[math]t_u + t_d = 4.5 = \frac {30}{15 + u} + \frac {30}{15 - u}[/math]

Multiplying both sides of the equation by [math]2(15 + u)(15 - u)[/math], we have:

[math]9(15^2 - u^2) = 60(15 - u) + 60(15 + u) = 1800[/math]

Dividing both sides of the equation by [math]9[/math]: [math]225 - u^2 = 200[/math]

Adding [math]u^2 - 200[/math] to both sides of the equation: [math]25 = u^2 \Rightarrow u = 5[/math]

Answer: Speed of stream is 5 km/hr.