And so, we can go ahead and graph our next data point. It's 0.5, of course, so, in here, that's about 0.5, and so that gives us an idea about where our next data point is.

There should be two milligrams left after 14.3 days so that's our point. And we could keep going, but this is enough to give you an idea of what the graph looks like.

- [Voiceover] Phosphorus-32 is radioactive and undergoes beta decay. Here's our beta particle, and the phosphorus is going to turn into sulfur.

Let's say we started with four milligrams of phosphorus-32. The half-life depends on what you're talking about.

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So as you increase the number of half-lives, you can see the amount of radioactive material is decreasing. If you start with four milligrams of phosphorus-32, how much is left after 57.2 days?

So if you're waiting 57.2 days, well, the half-life of phosphorus-32 is 14.3 days. 57.2 days divided by 14.3 days would give us how many half-lives, and that's four.

But this just helps you understand what's happening.Plot all data and connect them with the best fit line.Group Questions1) Francium 220 has a half-life of 27.5 seconds.Alright, we wait another 14.3 days, so we wait another half-life, so after two half-lives, that should be 28.6 days. Right, so if I think about this graph, this is exponential decay.So we know that after 28.6 days, it's another half-life, so what's 1/2 of two, it's one, of course. So after 28.6 days, we should have one milligram of our sample. That's what we're talking about when we're talking about radioactive decay here.