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Sagot :
Answer:
The speed of the boat is 9 miles/hour and the speed of the current is 3 miles/hour
Explanation:
Let's call x the speed of the boat and y the speed of the current.
The distance traveled is equal to the speed times the time, so the boat traveled 36 miles in three hours and we can write the following equation
(x + y)3 = 36
3(x + y) = 36
because when the boat traveled downstream, the total speed is the sum of x and y.
On the other hand, the boat traveled 30 miles upstream in 5 hours, so
(x - y)5 = 30
5(x - y) = 30
Therefore, the system of equations is
3(x + y) = 36
5(x - y) = 30
Solving the first equation for x, we get
[tex]\begin{gathered} 3(x+y)=36 \\ \\ \frac{3(x+y)}{3}=\frac{36}{3} \\ \\ x+y=12 \\ x+y-y=12-y \\ x=12-y \end{gathered}[/tex]Now, we can replace this expression on the second equation as follows
[tex]\begin{gathered} 5(x-y)=30 \\ \\ {\frac{5(x-y)}{5}}=\frac{30}{5} \\ \\ x-y=6 \\ \\ \text{ Replacing x = 12 - y} \\ 12-y-y=6 \\ 12-2y=6 \\ 12-2y-12=6-12 \\ -2y=-6 \\ \\ \frac{-2y}{-2}=\frac{-6}{-2} \\ \\ y=3 \end{gathered}[/tex]Then, the value of x is
x = 12 - y
x = 12 - 3
x = 9
So, the speed of the boat is 9 miles/hour and the speed of the current is 3 miles/hour
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