And that will give me a t value, a time of 119 seconds.

Again we really only know that to two significant figures.

So that'd be 1.2 times 10 to the 2 seconds.

Should it be less than the half life?

The half life was 230 seconds.

Well, yes, because the half life is to get to 50% complete, and

this is only 30% complete, so that number makes sense.

Now I wanna go back to the previous problem for just a moment, because if you

looked at this problem and you could not think, okay, 75% complete, that's two half

lives, you could work this problem in a similar fashion as the one before, and

if you started with 100 and at 75% complete, there's a 25 there.

And then we have a -k,

times t, and we could solve for t.

And we would find that it would be the same value.

So you didn't have to notice that it was two half-lives, but

once you know the half life it's sometimes very convenient to look for that.

Okay, so that finishes our learning objective.

We've learned the relationship between half life and k.

We can utilize that to go between the two, and then use it in a calculation.