volume-composite-figure-composed-of-cylinders

# Interactive video lesson plan for: Volume Composite Figure composed of Cylinders

#### Activity overview:

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How to find the volume of a composite figure composed of cylinders

This volume problem involves two cylinders but one is inside the other cylinder and making an impression. In this problem you subtract the volume of the two composite figures instead of adding.

Transcript

A composite of a cylinder inside a cylinder. Like a stck of washers or a stack of CD's. Same concept. First find the volume of the larger cylinder and subtract the volume of the smaller one. This time they are both circles so it will make the answer easier. We have a circle minis a circle. Think about your shapes and what you are subtracting. pi r squared times the height ( πr^2h - πr^2h) The formulas are the same, the only difference is that the radius will by different. What is the radius of the larger cylinder. It is 18. So eighteen squared times 12. Minus nine squared times 12.
18^2 x 12 = 3888π minus the other cylinder ( 9^2 x 12 = 972)
Can you subtract these. Yes because they both have a pi.
3888π - 972π = 2916π inches cubed.
So that is how you find the volume of composite figures when they are stacked on top of each other you add, and when one is inside the other and taking up space you subtract. Hope this was helpful.

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Tagged under: volume,composite figure,geometry,cylinder,volume cylinder,3d figure,volume 3d figures

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