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

(area)*(1+800/100) = (area)*9.

Hope it's clear.
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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:
GMAT assassins aren't born, they're made,
Rich
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i plugged in numbers...
r=1, diameter is 2.

area is pi. thus, new area would be 9pi.
9pi -> r=3, and diameter is 6.

to find the percent increase:
(6-2)/2 *100% = 4/2 *100% = 200%
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