00:01
From question a, i want to define a probability measure.
00:05
So a probability measure p is a function that assigns a probability to each event in probability space.
00:13
And so it satisfies three axioms.
00:18
One is non -negativity.
00:21
So for any event a, we must have p of a greater than or equal to 0.
00:28
2.
00:29
Normalization.
00:30
So p of omega sums up to 1, where omega is the sample space.
00:36
3.
00:37
Countable additivity or sigma additivity.
00:41
So for any countable sequence of disjoint events, a1, a2, ..., we must have p of infinite ai equals the sum of these probabilities.
00:59
Now, formally, let omega be the sample space, and f be a sigma -algebra subsets of omega, and p be a function, 0, 1, then p is a probability measure if it satisfies the three axioms above.
01:52
Above.
01:54
Okay, we can do 2.
01:58
We wanna show that p obeys the probability measure on.
02:02
So here the sample space is the interval 0 to 1, and the sigma algebra f is the boreal sigma algebra on , which consists of all boreal subsets of.
02:16
1.
02:32
Okay, and probability measure.
02:34
So, define p as the lebesgue measure on the interval 0 to 1.
02:47
And for any subset a in 0 to 1, p is the lebesgue measure of a, which corresponds to the length of a.
03:08
Now, we need to verify the three axioms of probability measure.
03:13
So, we have 4oa a in f, p of a is greater than or equal to 0, and the lebesgue measure of any set a is always non -negative.
03:25
Normalization, probability 0, 1 is equal to 1, because the lebesgue measure of the interval 0 to 1 is 1.
03:35
Countable additivity.
03:37
So for any sequence a1 through a1, a2, ...
03:46
In f, we have ai equals infinite p of ai.
04:00
So the lebesgue measure satisfies the accountable additivity.
04:04
And if set ai is a countable collection of these joint sets in the interval 0 to 1, then the measure of the union is the sum of the measures.
04:17
So this one is satisfied...