Question

From a solid cylinder of height 2.8 cm and diameter 4.2 cm, a conical cavity of the same height and same diameter is hollowed out. Find the total surface area of the remaining solid.(use π = \(\frac{22}7\))

Answer 1

Slant height of the cone, l = \(\sqrt{(2.8)^2 + (2.1)^2}\) = 3.5 cm

Remaining area of the cylinder = Curved surface area of the cylindrical part + Area of the conical part + Area of cylindrical base 

= 2πrh + πrl + πr² 

= 2π × (2.1)× (2.8) + π × 2.1 × (3.5) + π (2.1)² 

= 36.96 + 23.1 + 13.86 

= 73.92 cm²

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