A) \[780\,c{{m}^{2}}\]
B) \[770\,c{{m}^{2}}\]
C) \[715\,c{{m}^{2}}\]
D) \[660\,c{{m}^{2}}\]
Correct Answer: B
Solution :
Let \[{{r}_{1}}\] and \[{{r}_{2}}\] be the radius, \[\therefore \] \[2\pi {{r}_{1}}=88\,cm\] and \[2\pi {{r}_{2}}=132\,cm\] \[\Rightarrow \] \[{{r}_{1}}=14\,cm\] and \[{{r}_{2}}=21\,cm\] \[\therefore \] Area of ring \[=\pi (r_{2}^{2}-r_{1}^{2})\] \[=\frac{22}{7}({{21}^{2}}-{{14}^{2}})\] \[=\frac{22}{7}(144-196)=770\,c{{m}^{2}}\]
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