Question

please solve this!!
thanks!!

Answer 1

consider outside circle's radius = R
 consider inside circle's radius = r
given 
R-r=7cm  ->(i)
difference in areas pi*R-pi*r=1078cm^2
taking pi common
pi(R^2-r^2)=1078
pi(R-r)(R + r)=1078
pi(7)(R + r)=1078                          :given R-r=7
R + r=49   (approx)->(ii)
adding both the equations I and ii
R + r + R - r = 49+7
2R=56
R=28cm
r=21cm
voila!!!

Answer 2

pi (r+7)2 - pi r2= 1078
22/7×((r2+49+14r)-r2)=1078
r2+49+14r-r2=1078×7/22=343
49+14r=343
14r=343-49=294
r= 294/14=21
r=21cm


may this help u