The height of a cone is two times its base diameter. What is the volume of the cone in terms of its base radius r?
V = r2
V = r3
V = r3
V = r2

Question

The height of a cone is two times its base diameter. What is the volume of the cone in terms of its base radius r?
V =   r2
V =   r3
V =   r3
V =   r2

mathmale · Answer

The formula for the volume of a cone is $$V=\frac{ 1 }{ 3 }b h$$

But since the area of the base, b, is $$\pi r^2$$

mathmale · Answer

We get the formula $$V=\frac{ 1 }{ 3 }[\pi r^2]h$$

mathmale · Answer

You are told that the height of the cone is 2 times the base diameter.  
The base diameter is 2r.

What is h=2 times the base diameter, 2r?   h= ?

Substitute this result into the last volume formula above.