A) 4 cm
B) 3 cm
C) 3.5 cm
D) 5 cm
Correct Answer: B
Solution :
[b] Let the original radius = r \[\therefore \] \[Area\,A=\pi {{r}^{2}}\] Increased area \[A'=\pi {{(r+1)}^{2}}\] Now, \[A'=A+22\] \[\pi {{(r+1)}^{2}}=\pi {{r}^{2}}+22\] \[\Rightarrow \] \[\pi {{[(r+1)]}^{2}}-{{r}^{2}}]=22\] \[\Rightarrow \] \[\pi [(r+1+r)(r+1-r)]=22\] \[\Rightarrow \] \[\pi (2r+1)=22\] \[2r+1=\frac{22\times 7}{22}\] \[\left[ \because \,\,\,\pi =\frac{22}{7} \right]\] \[\Rightarrow \] \[2r+1=7\] \[\Rightarrow \] \[2r=6\] \[\Rightarrow \] \[r=3\,cm\]
You need to login to perform this action.
You will be redirected in
3 sec
