There is a hollow cylinder as shown in the figure having outer radius 7 cm, height 21 cm and inner radius 6 cm, whose inner and outer surfaces are to be painted. Calculate the area to be painted.

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Solution

Area to be painted = inner curved surface area + outer curved surface area
Let inner radius be $r_{1}$ and outer radius be $r_{2}$ .
Required area = Curved surface area of the hollow cylinder = $2 π r_{1} h + 2 π r_{2} h$
$A r e a = 2 π h (r_{1} + r_{2})$
$A r e a = 2 \times \frac{22}{7} \times 21 (7 + 6)$
= $1716 c m^{2}$

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There is a hollow cylinder as shown in the figure having outer radius 7 cm, height 21 cm and inner radius 6 cm, whose inner and outer surfaces are to be painted. Calculate the area to be painted.

Area to be painted = inner curved surface area + outer curved surface area Let inner radius be r1 and outer radius be r2 . Required area = Curved surface area of the hollow cylinder = 2πr1h+2πr2h Area=2πh(r1+r2) Area=2×227×21(7+6) = 1716 cm2