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2 years ago

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If a person rows to his favorite fishing spot 21 miles downstream in the same amount of time that he rows 7 miles

1 answer:

klio [65]2 years ago

8 0

28 miles upstream requires 28/7 = 4 hours.

28 miles downstream requires 28/21 = 4/3 hours, or 1 hour and 20 minutes.

How long does it take him to cover 28 miles?

Apply the distance formula:

d = rt

where

d is distance

r is rate or speed

t is time

21 = t*(r+7) = rt+ 7t

7 = t *(r-7) = rt - 7t

28 = 2rt

14 = rt

21 = rt + 7t

21 = 14 + 7t

7 = 7t

t=1

21 = (r+7)*1 = r+7

r = 14

The speed of the boat is 14 mph. With the current (downstream), the speed is 14+7 = 21 mph, so 21 miles are traveled in 1 hour. Against the current (upstream), the speed is 14-7 = 7 mph, which means 7 miles are traveled in the same 1-hour time frame.

28 miles downstream requires 28/21 = 4/3 hours, or 1 hour and 20 minutes.

28 miles upstream requires 28/7 = 4 hours.

To learn more about sequences refer to:

brainly.com/question/340538

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Step-by-step explanation:

Given

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Divide through by π

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Make h the subject:

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Surface Area (A) of a cylinder is calculated as thus:

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Factorize:

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To minimize, we have to differentiate both sides and set $A' = 0$

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Cross Multiply

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Divide through by 2

$r^3 = 216$

Take cube roots of both sides

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$h = \frac{432}{6^2}$

$h = \frac{432}{36}$

$h = 12$

Hence, the dimension that requires the least amount of material is when

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