Find the area to be painted in the following block with a cylindrical hole. Given that length is 15cm, width 12cm, height 20cm and radius of the hole 2.8cm.

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Solution

Length of the given figure = 15 cm
Width of the given figure = 12 cm
Height of the given figure = 20 cm
Radius of the hole = 2.8 cm
$∴$ The area to be painted = Surface area of the figure - 2 $\times$ Area of the circular hole
$= 2 (l b + b h + l h) - 2 π r^{2} = 2 (15 \times 12 + 12 \times 20 + 15 \times 20) - 2 \times \frac{22}{7} \times 2.8 \times 2.8 = 2 (180 + 240 + 300) - \frac{44 \times 2.8 \times 2.8}{7} = 2 \times 720 - 49.28 = 1440 - 49.28 = 1390.72 c m^{2}$

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