 The last two problems on your note sheet involve using cones. So in number six we have a cone that has an altitude of 8 and a diameter of 2.5. We want to find the approximate volume. So I'm going to start with giving a pen, there we go. The volume of a cone is one-third times the area of the base times the height. And of course the base of the cone is pi r squared times the height of the cone. And if I'm taking a look at what I've been given, remember altitude is just another word for height. So I know that the height of this cone is 8 and the radius is going to be half of the diameter. So if the diameter is 2.5 that the radius would be 1.25. So plugging in the numbers, one-third times pi times 1.25 squared times 8 and you can put it in your calculator, approximate answer should be 13.1 and this would be cubic inches. Number seven, they give us the volume and are asking us to find the radius. So this is another problem where we're working backwards to solve for r. So we're going to start with our volume formula, volume of a cone is one-third times the area of the base which is pi r squared times the height of the cone. They tell us what the volume is so I'm going to plug in 480 pi for the volume equals one-third pi r squared because we don't know what r is times 10 because they tell us that the height is 10. Now the easiest way to do this problem when you're solving this is to get rid of that fraction and to get rid of a fraction remember we always multiply by the reciprocal. So multiply both sides by 3. You get 1440 pi equals pi r squared times 10. And so now we can get rid of the 10 and the pi, so divide by 10 pi, divide the other side by 10 pi. What happens is on this side the 10 and the pi cancel out so we're left with r squared and over here the pi's cancel each other out and 1440, 1440 divided by 10 is 144. So then we can square root both sides and we get a radius of 12 units.