 Okay, ladies, let's try to do some density problems now. So let's do this first problem, calculating the density of a solid. So usually solids are measured, their volume is measured in a centimeter's cube because you can actually measure with a ruler or whatever. So let's just read this problem. It says, as opposed to liquids and gases, liquids volumes are usually measured in, milliliters are liters, and gases are usually measured in liters. But anyways, so it says 2.00 centimeter cubed block of aluminum is found to weigh 5.40 grams. The density of aluminum in units of grams per centimeter cubed. So remember, we want to first write down the numbers that are given to us in the problem with the correct units. So the volume, we said, was 2.00 centimeters cubed, and it also gave us the mass, and that was 5.40 grams. So I know, I just taught you how to memorize the density formula, so how to do density with this formula. Density equals mass divided by volume. But the problem said, give the solution in units of grams per centimeters cubed. So that should give you a clue as to how to set up this formula, even if you didn't know this. Even though you've already memorized this, we've already said that. But it told you, well, give it to you in grams per centimeter cubed. But it didn't show it like that in the problem. Remember, it shows it like this in the problem, and that's what we say like the text message way of writing this same thing here. So if you didn't remember this, you could remember just from what the problem was saying, that the density is, well, you put the grams on top of the centimeters cubed, right? So 5.40 grams and 2.00 centimeters cubed. And then you just use your calculator and calculate it, 5.40 divided by 2. And that gives you 2.7 on the calculator. But of course, remember, 3 significant figures, 3 significant figures. So we're going to go 2.70 grams per centimeter cubed. And then we'll write it this way in our final answer, because that's the preferable way of writing it. So that's how to find the density of the solid. And again, remember, solids are a lot of times given in volumes of centimeters cubed or meters cubed or things like that, just because it's easier to measure that than the milliliters or whatever. And we'll talk about gases and liquids in like two seconds. Okay? Cool.