00:01
When i do half -life problems, i like to set up my equation like this, where you have the initial amount and your base is one -half to the t over k power.
00:11
So when you're looking at that we start with 304 grams, so 304, it's still one -half right here.
00:21
Let's see, we're going to actually we know we're going to solve for k, let me put it that way.
00:30
And we know that after 255 minutes, that's how long it takes before we get down to 38 grams.
00:39
So what you want to do next is divide the 304 over.
00:45
And what i like to do is the natural log on both sides.
00:49
And you can reduce this or you can leave it alone.
00:51
And you can actually do any log that you want.
00:55
And the reason for that is we can use the law of logs where we can move the exponent in front.
01:05
I just like waiting until the end to use my calculator.
01:10
Because now you can do, you cross -multify, so multiply the k to the right side.
01:15
I'm just writing it like this...