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3 years ago

11

A motorboat can go 8 miles downstream on a river in 20 minutes. It takes 30 minutes for the boat to go upstream the same 8 miles

. Find the speed of the current

2 answers:

ladessa [460]3 years ago

6 0

Answer:

<em>The speed of the current is </em><em>4 miles/hour</em>

Step-by-step explanation:

Let us assume that,

x = speed of the boat,

y = speed of the current.

We know that,

$\text{Speed}=\dfrac{\text{Distance}}{\text{Time}}$

A motorboat can go 8 miles <em>downstream</em> on a river in 20 minutes or $\dfrac{20}{60}$ hours.

$\Rightarrow x+y=\dfrac{8}{\frac{20}{60}}=\dfrac{8\times 60}{20}$

$\Rightarrow x+y=24$ --------------------------1

It takes 30 minutes for the boat to go <em>upstream</em> the same 8 miles.

$\Rightarrow x-y=\dfrac{8}{\frac{30}{60}}=\dfrac{8\times 60}{30}$

$\Rightarrow x-y=16$ ----------------------------2

Subtracting equation 1 and 2,

$\Rightarrow x+y-x+y=24-16$

$\Rightarrow 2y=8$

$\Rightarrow y=4$ miles/hour

sasho [114]3 years ago

3 0

4 miles per hour is the answer

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2 years ago

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Y_Kistochka [10]

Answer:

A = 374.123 ft^2

Step-by-step explanation:

First, lets calculate the perimeter:

Perimeter (p) = side length (s) * number of sides (n)

$p = s * n$

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$p = 72$

Next, lets find the apothem, which is the shortest length from any side to the middle. It's like the radius in a circle, but more complicated.

Apothem (a) = side length (s) / ( 2 * tan(180/number of sides (n)) )

$a = \frac{s}{2 * tan (\frac{180}{n} )}$

$a = \frac{12}{2 * tan (\frac{180}{6} )}$

$a = \frac{12}{2 * \frac{\sqrt{3} }{3}}$

$a = \frac{12}{\frac{2\sqrt{3} }{3}}$

$a = \frac{12*3}{2\sqrt{3}}$

$a = \frac{6*3}{\sqrt{3}}$

$a = \frac{18}{\sqrt{3}}$

Now, finally, to find the area of a regular polygon, we use the following equation:

Area (A) = ( apothem (a) * perimeter (p) ) / 2

$A = \frac{a * p}{2}$

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Turning into a decimal:

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8 0

3 years ago