 So, how many grams do 20 calcium atoms weight? Okay? So, 20 calcium. How many grams do they weight? So, let's write down what the problem says. So, we've got calcium at 20 atoms. So, what do we know about one atom of calcium and how much it weighs? So, we look at the periodic table and we've got a conversion, right? And one atom of calcium equals 40.08, we'll say, AMU, right? So, we're doing okay with that. And we already know this, a converter detector was given to us one AMU to grams, right? So, we should be able to put these two in a row to get this mass. Is everybody okay with that? So, it gave us, the problem gave us the number of calcium atoms, right? So, we'll say 20 calcium. So, again, it's good for you to, you know, if you're having trouble with what units go on the bottom, go on the top, write the whole thing out. So, the problem, sorry, the problem gave us, when it's 20 like this, right, I should have said something. That's an infinite number of significant figures, okay? Because it's just like counting, how many students do I have in this room? 1, 2, 3, 4, 5, 6, 7, 8, not 8.3 something, okay? So, that's an infinite number of significant figures. So, in actuality, this problem, you could give it to as many significant figures as you want, finally, if that's the case, okay? It's common to go to like 3 or 4. So, anyways, so do we have a conversion that goes from atoms to AMU? Yes. So, 1 atom calcium is 40.08 or 1 calcium atom. And then, of course, we do the conversion factor that we used in the problem previous and say 1 AMU at the bottom, 1.661 times 10 to the negative 24 grams on the top. So, will we expect this to be a lot of grams or a tiny amount of grams? Small amount, right? A small amount, because 4 calcium atoms is very tiny, right? Very tiny, or 20 calcium atoms, very tiny. 4 is also very tiny, okay? So, let's just plug in, right? So, 20 times 40.08. And so, this one you would expect to get a negative exponent, okay? So, again, I'm going to take this as a 4-6 fix just because 1.331 times 10 to the negative 21 grams, okay? So, that's how many grams, 20 calcium atoms, weighs. Hopefully, it makes sense, right? Because that's very much smaller than 1 gram.