Multiple choice

A circle of radius 9 cm has its radius decreased by 2 cm. What is the approximate percentage decrease in area?

  1. 40

  2. 60

  3. 31.5

  4. 39.5

  5. None of these
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D Correct answer
Explanation

Initial area = pi * 9^2 = 81pi. New radius = 7, new area = 49pi. Decrease = 81 - 49 = 32. Percentage decrease = (32/81) * 100 = 39.506%.

AI explanation

Using the area of a circle formula, the initial area is pi times 9 squared which is 81 pi, and the new area is pi times 7 squared which is 49 pi. The decrease in area is 81 pi minus 49 pi, giving 32 pi. To find the percentage decrease, we calculate 32 pi divided by 81 pi and multiply by 100, which equals approximately 39.5 percent.

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