A) \[98\pi \,\,c{{m}^{2}}\]
B) \[106\pi \,\,c{{m}^{2}}\]
C) \[108\pi \,\,c{{m}^{2}}\]
D) \[110\pi \,\,c{{m}^{2}}\]
Correct Answer: D
Solution :
External diameter of cylinder = 7 cm \[\therefore \]External radius\[=\frac{7}{2}\,\,cm\] \[\therefore \]Internal diameter\[=7-2\] \[=5\,\,\text{cm}\] Internal radius\[=\frac{5}{2}\,\,\text{cm}\] Total external surface area of cylinder \[=2\pi Rh+2\pi ({{R}^{2}}-{{r}^{2}})\] \[=2\pi \times \frac{7}{2}\times 14+2\pi \left[ {{\left( \frac{7}{2} \right)}^{2}}-{{\left( \frac{5}{2} \right)}^{2}} \right]\] \[=98\pi +12\pi =110\pi \,\,c{{m}^{2}}\]
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