00:01
So in this question, we're told that we have a total population of the 1 million people.
00:07
So p total equals 1 in units of millions.
00:15
Now, p of t is the number of people who are aware of the product, who become aware of the product by time t.
00:28
So the total number of people who are aware by time t.
00:42
Now we're told that p increases a rate proportional to the number of people who are still unaware of the product.
00:55
So the number of people still unaware of the product is 1 minus p of t, and this is just a proportionality constant.
01:03
Now we're also told that nobody was aware of the product at the beginning of the campaign, and that after 20 days of advertising, 50 % of people were aware.
01:18
So now we can solve this differential equation.
01:21
So the integral of p over 1 minus p is going to be equal to the integral of adt.
01:33
And at time t equals zero, nobody is aware of the product.
01:39
And then at time t equals t, we're going to have p of t.
01:44
People are going to be aware.
01:47
So let's integrate this.
01:49
So this is going to be log of 1 minus p.
01:55
With a minus sign because the derivative of this is going to be minus 1 over 1 minus p.
02:01
Now putting in these two boundary conditions, it's just the same as evaluating this at each of the boundary conditions and dividing them.
02:13
But i'll save that for a minute...