00:01
Okay, so we're given a half -life here.
00:03
So let's go ahead and use our half -life to find k.
00:07
We know half -life is l -n -of -2 over k, so k is going to equal the l -n -of -2 over our half -life.
00:19
So l -n -2 is 0 .693.
00:23
And we'll divide that by our half -life, which is 5 .27 years.
00:28
And we'll get our k is 0 .131.
00:32
And the years to the negative 1 here.
00:36
Now we're going to plug into our equation ln of a0 over a is kt.
00:47
So they said we went from where we were to 18%.
00:52
So i'm going to call the original 1 and then the final at time t to be 0 .18 or 18 % of that.
01:01
So that's 0 .131 times time.
01:10
So our time is going to come out to be 13 .1 years...