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The height of a solid cylinder is 30 cm and the diameter of its base is 10 cm. Two identical conical holes each of radius 5 cm and height 12 cm are drilled out. What is the surface area (in cm2) of the remaining solid?

The height of a solid cylinder is 30 cm and the diameter of its base is 10 cm. Two identical conical holes each of radius 5 cm and height 12 cm are drilled out. What is the surface area (in cm2) of the remaining solid? Correct Answer 430π

Given:

Height of cylinder = 30 cm

Radius of cylinder = 5 cm

Height of cone = 12 cm

Radius of cone = 5 cm

Formula used:

The surface area of cylinder = 2πrh

The surface area of cone = πrl

l2 = h2 + r2

Where,

l = slant height of the cone

h = height

r = radius

Calculation:

Additional Information

When the cones are drilled out then the volume of a cylinder is decreasing. But the surface area will increase. Surface area means the area which we can touch.  When the cones drilled out then we can touch both outer and the inner surface. So we have to add both surface areas. 

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