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7.A closed cylindrical tank of radius 7 m and height 3 m is made from a sheet of metal. How much sheet of metal is required?
Answer :

Given, r = 7 m and h = 3 m.
Sheet required to make a closed cylinder= Total surface area of the cylinder

\(= 2\pi r(r + h)\) sq. units

\(=2\times \frac { 22 }{ 7 } \times 7\times (3+7)\)

\(=2\times \frac { 22 }{ 7 } \times 7\times 10 \)

\(=440 m^2\)

So, the required metal sheet=\(440m^2\)