Finding percentage increase in area of a circle when the radius is increased by a certain percent

1] If radius of a circle is increased by 100%,then the area is increased by
a] 100%  b] 200%  c]300%  d]400%                                                                                  

Solution
let the original radius be R cm

New radius = {(100+100)/100}R cm = (200/100) R = 2R cm

original area = pi * R^2  cm^2

New area =  pi * (2R)^2  cm^2

change in area = pi *4* R^2 -  pi  * R^2 = 3 * pi * R^2

% increase in area =  3 * pi * R^2 * [1/ pi  * R^2 ] * 100 =300 %                       
                          
Practice questions

2] If radius of a circle is increased by 6%,then the area is increased by
a] 12.36%  b] 12.35%  c]12.34%  d]12.33%         

*3] If radius of a circle is doubled,how many times of the area of original circle will it become now?
a] 100%  b] 200%  c]300%  d]400%       
 
4] If radius of a circle is increased by 1%,what is the increased percent in the area 
a] 1%  b] 2%  c]1.1%  d]2.01%