00:02
We're given a probability function, p of t, and in this function, t is the number of minutes, and p is the probability that the event will occur within that number of minutes, so within t minutes.
00:17
And our task is to determine after how many minutes, right, so t equals what, for the probability to equal 50%, which 50 % is 50 out of 100, which is 0 .5.
00:32
And then we're also tasked with determining after how many minutes the probability will have gotten up to 80%, which is 80 out of 100 is 0 .8.
00:45
So we're going to have to do the same thing twice.
00:48
Why not derive a formula t in terms of p? and then we could use that formula twice.
00:54
That would be more efficient.
00:56
So we're going to take our probability formula and solve it for t.
01:01
So the first thing we're going to do is subtract one from both sides.
01:04
And then we're also going to multiply both sides by negative one.
01:09
And that will isolate our exponential.
01:14
And then we're going to take the natural log of both sides.
01:17
So while we're at it, let's distribute this minus one.
01:20
Negative p plus one, well, it's one minus p, is equal to the natural log of e to the negative 0 .15t...