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The radius of a circle has been reduced from 9 cm to 7 cm . the appropriate percentage decrease in area is ?
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- 31.5 %
- 39.5 %
- 34.5 %
- 65.5 %
Correct Option: B
Original area = (22/7) x 9 x 9 cm2
New area = (22/7) x 7 x 7 cm2
∴ Decrease = 22/7 x [(9)2 -(7)2] cm2
=(22/7) x 16 x 2 cm2
Decrease percent = [(22/7 x 16 x 2) /( 7/22 x 9 x 9)] x 100 %
= 39.5 %
