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प्रश्न
Find the area to be painted in the following block with a cylindrical hole. Given that length is 15 cm, width 12 cm, height 20 cm and radius of the hole 2.8 cm.
उत्तर
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 × Area of the circular hole
= 2(lb + bh + lh) – 2πr2
= `2(15 xx 12 + 12 xx 20 + 15 xx 20) - 2 xx 22/7 xx 2.8 xx 2.8`
= `2(180 + 240 + 300) - (44 xx 2.8 xx 2.8)/7`
= 2 × 720 – 49.28
= 1440 – 49.28
= 1390.72 cm2
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