Question

On decreasing the radius of a circle by 30%, its area is decreased by

विकल्प

• 30%

• 60%

• 45%

• none of these

Answer 1

None of these

Let r be the original radius.

Thus, we have:

Original area = πr²

Also,

New radius = 70% of r

`=(70/100xx""r")`

`= (7"r")/10`

New area `= pixx((7"r")/10)^2`

`= (49pi"r"^2)/100`

Decrease oin the area`=(pi"r"^2 = (49pi"r"^2)/100)`

`=(59pi"r"^2)/100`

Thus, we have;

Decrease in the area`=((59pi"r"^2)/100xx1/pi"r"^2xx100)%`

                                = 51%