The speed of the current in a river is 6mph. A ferry operator who works that part of the river is looking to buy a new boat for
her business. Every day, her route takes her 22.5 miles each way against the current and back to her dock, and she needs to make the trip in a total of 9 hours. She has a boat in mind, but she can only test it on a lake where there is no current at all. How fast must the boat go on the lake in order for it to serve the ferry operator's needs?
1 answer:
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Answer:
Step-by-step explanation:
step 1
Find the area of the plate
The area of a circle is given by the formula
we have
---> the radius is half the diameter
substitute
step 2
Find the area of the square napkin folded (is a half of the area of the square napkin)
we know that
The diagonal of the square is the same that the diameter of the plate
Applying Pythagorean theorem
where
b is the length side of the square
we have
substitute
solve for b^2
-----> is the area of the square
Divide by 2
step 3
Find the area of the space on the plate that is NOT covered by the napkin
we know that
The area of the space on the plate that is NOT covered by the napkin, is equal to subtract the area of the square napkin folded (is a half of the area of the square napkin) from the area of the plate
so
simplify