Q19 of 47 Page 1

In Fig. 5, from a cuboidal solid metallic block, of dimensions 15 cm × 10 cm × 5 cm, a cylindrical hole of diameter 7 cm is drilled out. Find the surface area of the remaining block.


Total Surface area of cuboide (before drilling) = 2(lb + bh + lh)

T.S.A. cuboid = 2(15 × 10 + 10 × 5 + 15 × 5) = 2(275) = 550cm2


Radius of cylindrical hole = 7/2 = 3.5cm




Surface Area of remaining block = (Total surface Area of cuboid)


-(Area of two circular bases)


+ (Curved surface area of cylinder)


Surface area of remaining block = 550-77 + 110 = 583cm2


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