00:01
So in this question, we have s is the event that you're a safe driver.
00:09
So sc is going to be the event that you're an unsafe driver.
00:16
And we have the probability of having an accident.
00:19
So let's say that a is the event that you have an accident, and ac is the event that you have no accident.
00:29
We're told that 70 % of the population are safe.
00:32
So ps is 0 .7.
00:34
And if you're safe, you have a probability of 0 .1 of causing an accident.
00:44
But if you're not safe, then the probability of having an accident is 0 .5.
00:54
Now the insurance premium is $400 times the probability of having an accident in the following year for a particular person.
01:14
Now a new subscriber has an accident during the first year.
01:19
So what should their insurance premium be for the next year? so what's the probability of having an accident in the second year, given that you have an accident in the first year? well, that's going to be the probability of having an accident in the second year, given that you're safe, times the probability that you're safe, given that you had an accident in the first year, plus the probability of having an accident in the second year, given that you're not safe, times the probability that you're not safe, given that you had an accident in the first year.
01:58
So we need to work out, what are the probabilities of being safe or unsafe, given that you had an accident? well, the probability of being safe, given that you have an accident, is the probability of having an accident, given that you're safe, the probability of being safe, over the probability of having an accident, which we can decompose in this way...