The area of the circle is increased by 800%, thus the area is increased 9 times.

The area of a circle it proportional to the square of the diameter (\(area=\pi{\frac{d^2}{4}}\)), therefore the diameter must increase 3 times (diameter increase 3 times = area increase 9 times), which is increase by 200%.

Answer: B.

Similar questions to practice:
at-a-certain-pizza-parlor-the-diameter-140460.html
the-weight-of-a-hollow-sphere-is-directly-dependent-on-its-142327.html

Hope it helps.
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How did you figure "The area of the circle is increased by 800%, thus the area is increased 9 times" ?

Hi All,

There's a practical way to prove the correct answer. We can TEST VALUES, using the answer choices to limit our TESTs:

If we have a circle with....
A diameter of 2
it's radius = 1
it's area = (1^2)pi = 1pi

Answer A:
If we increase that diameter 100%, we have....
A diameter of 4
it's radius = 2
it's area = (2^2)pi = 4pi
This area has increased (4pi - 1pi)/1pi = 3pi/1pi = 3 = 300%

Answer B:
If we increase the diameter 200%, we have...
A diameter of 6
it's area = 3
it's area = (3^2)pi = 9pi
This area has increased (9pi - 1pi)/1pi = 8pi/1pi = 8 = 800%

This is a MATCH for what we're looking for!

Final Answer:

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