hello saiprasad,

i will give u general solution so u can do any question of these type using the solution(this will be helpful in you jee as well)

Let the mass of the disc = M 
Therefore, the mass of the removed part of disc, m = (M/R^2)*(R/2)^2 = M/4 
Now the center of gravity of the resulting flat body, 
R= [M*0 – (M/4)*(R/2)]/(M-M/4) 
= -(MR/8)/(3M/4) 
= -R/6 
Negative sign shows that the center of gravity lies at opposite direction of the original COM at a distance R/6.