Question

The radius of a circle has been reduced from 9 cms to 7 cms. The
approximate percentage decrease in area is:
a) 31.5%
b) 39.5%
c) 34.5%
d) 65.5%

Answer 1

Answer:

Step-by-step explanation:

Area of circle When radius is 9 cm:

circle 1= 3.14*R*R

(  where R is the radius of first circle & 3.14 is pi value it will be constant all time )

so,

      = 3.14*9*9

     =254.34

Now we calculate other circle area which radius is reduced by 2 cm;

 circle2=3.14*R*R

(  where R is the radius of first circle & 3.14 is pi value it will be constant all time )

circle2=3.14*7*7

          =153.86

difference between two area = circle1-circle2

                                                 =254.34-153.86

                                                 =101

Change in percentage id given by=

                             (Difference between two area)/Area of circle1*(100)

                             =101/254.34*100

                              =39.5%