The height of a solid cylinder is 30 cm and the diameter of its base is 10 cm. two idendical 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?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 430 π
Concept
Remaining surface area = Surface Area of the figure + No. of Area of new surface drilled out
Application
l2 = h2 + r2
l2 = 122 + 52
l2 = 144 + 25
l = 13 cm
Since there are two new cones drilled out and we can surely touch them. The surface are of the remaining firgure can be calculated as
The surface area of the remaining figure = surface area of cylinder + 2 × surface area of the cone
2πrh + 2πrl
2πr(h + l)
2π × 5(30 + 13)
430π