Geometry!

Geometry Level 3

From a circular cylinder of diameter 10 cm and height 12 cm conical cavity of the same base radius and of the same height is hollowed out .Find the sum of the numerical values of the volume and the whole surface area of the remaining solid (take pi = 3.14)


The answer is 1287.4.

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1 solution

The volume of the remaining solid is equal to the volume of the right circular cylinder minus the volume of the right circular cone. We have

V = V [ c y l i n d e r ] V [ c o n e ] = π r 2 h 1 3 π r 2 h = π ( 5 2 ) ( 12 ) 1 3 ( π ) ( 5 2 ) ( 12 ) = 200 π V=V[cylinder]-V[cone]=\pi r^2h - \dfrac{1}{3}\pi r^2 h = \pi (5^2)(12)-\dfrac{1}{3}(\pi)(5^2)(12)=200 \pi

The total surface area of the remaining solid is equal to the curved surface area of the cone plus the curved surface area of the cylinder plus the area of the base. We have

A = π r L + 2 π r h + π r 2 = π ( 5 ) ( 13 ) + 2 ( π ) ( 5 ) ( 12 ) + π ( 5 2 ) = 65 π + 120 π + 25 π = 210 π A=\pi rL+2\pi r h+ \pi r^2= \pi (5)(13)+ 2(\pi)(5)(12)+ \pi (5^2)=65 \pi + 120 \pi + 25 \pi = 210 \pi

So the numerical sum is

V + A = 200 π + 210 π = 410 π = 410 ( 3.14 ) = 1287.4 V+A= 200 \pi + 210 \pi = 410 \pi = 410 (3.14) = \boxed{1287.4}

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