Question

The radius of a circle has been reduced from 9 cm to 7 cm. The approximate percentage decrease in area is:

Answer 1

Answer:

Step-by-step explanation:

Original area = π x (r/2)2 = πr2/4

Reduction in area = π r2 - 3π r2/4

∴ Reduction per cent = [ 3πr2/4 x 4/(πr2) x 100 ] %

= 75%

Answer 2

The approximate percentage decrease in area is 39.50%

Step-by-step explanation:

Original radius = 9 cm

Area of original circle =$\pi r^2 = 3.14 \times 9^2 = 254.34 cm^2$

Reduced radius = 7 cm

Area of reduced circle = $3.14 \times 7^2 =153.86cm^2$

Change in area = 254.34 - 153.86 =100.48  sq.cm.

The approximate percentage decrease in area =$\frac{100.48}{254.34} \times 100 =39.50\%$

Hence The approximate percentage decrease in area is 39.50%

#Learn more:

The  Radius  of  sphere  is  increased from 7cm  to 7.02 cm.  find  The  Approximate  increase in  Volume.​

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