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Geometry and Trigonometry Difficulty: Medium

A cylinder has a diameter of 8 inches and a height of 12 inches. What is the volume, in cubic inches, of the cylinder?

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Explanation

Choice C is correct. The base of a cylinder is a circle with a diameter equal to the diameter of the cylinder. The volume, V , of a cylinder can be found by multiplying the area of the circular base, A , by the height of the cylinder, h , or V=Ah. The area of a circle can be found using the formula A=πr2, where r is the radius of the circle. It’s given that the diameter of the cylinder is 8 inches. Thus, the radius of this circle is 4 inches. Therefore, the area of the circular base of the cylinder is A=π42, or 16π square inches. It’s given that the height h of the cylinder is 12 inches. Substituting 16π for A and 12 for h in the formula V=Ah gives V=16π12, or 192π cubic inches.

Choice A is incorrect. This is the area of the circular base of the cylinder.

Choice B is incorrect and may result from using 8 , instead of 16 , as the value of r2 in the formula for the area of a circle.

Choice D is incorrect and may result from using 8 , instead of 4 , for the radius of the circular base.