 Okay, so let's try this problem. It's like an Avogadro's number problem. It says how many moles of potassium are in 1.25 times 10 to the 21st atoms of potassium? Okay, so this is just a simple conversion actually, but in order to do it, you've got to know what conversion factor to use. Okay, and you're going to have to use Avogadro's number. Avogadro's number will be given to you on the quiz or exam, so it's one mole, in this case, of potassium equals 6.022 times 10 to the 23rd atoms of potassium like that. So we've got the number of atoms of potassium, and we want the number of moles of potassium. Okay, so the number of moles of potassium, well, we're just going to say 1.25 times 10 to the 21st atoms of potassium. And do we have a conversion factor that'll convert that to moles? Written up there? Yes, we do. Okay, so all we're going to do is multiply that. What units are we going to put on the bottom? Atoms of potassium. Okay, so which number is that? 1 or 6.022? Yeah, the 6.022. So how did I know that one had to be on the bottom? Because I have to cancel out my units. Okay, so you're having a hard time with that, deciding which one. You're always going to get the wrong answer unless you just happen to be lucky. Okay, so make sure you know you're canceling these units out to get the other units. That's what we're trying to do. Okay, so now all it is is just plug them into your calculator and you're done. Okay, so 1.25 e to the 21 divide that by Avogadro's number, 6.022 e to the 23rd. I get what is a small number, as you would expect, 2.08 times 10 to the negative 3 moles of potassium. So that's how many moles of potassium there are and that many atoms of potassium, 1.25 times 10 to the 24th. Okay, questions on that one? Can I kill it?