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- UK Year 13 Maths
- Probability

Still Confused?

Try reviewing these fundamentals first.

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That's that last lesson.

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Get Started NowStart now and get better math marks!

Get Started NowStart now and get better math marks!

Get Started NowStart now and get better math marks!

Get Started Now- Intro Lesson: a8:46
- Intro Lesson: b7:09
- Lesson: 110:03
- Lesson: 26:54
- Lesson: 39:07

Recall:

P(*A* and *B*)=P(*A*)$\cdot$P(*B*|*A*) or equivalently, P(*A* and *B*)=P(*B*)$\cdot$P(*A*|*B*)

__The Law of Total Probability:__

*P(A)=P(A and B)+P(A and ~B)=P(B)P(A|B)+P(~B)P(A|~B)*

Or in full generality, if all of $B_1, B_2,...B_n$ include the entire sample space S, and are all pairwise mutually exclusive then:

$P(A)=P(A$ and $B_1)+P(A$ and $B_2)+ \cdots +P(A$ and $B_n)$

$=P(B_1)P(A|B_1)+P(B_2)P(A|B_2)+ \cdots + P(B_n)P(A|B_n)$

P(

Or in full generality, if all of $B_1, B_2,...B_n$ include the entire sample space S, and are all pairwise mutually exclusive then:

$P(A)=P(A$ and $B_1)+P(A$ and $B_2)+ \cdots +P(A$ and $B_n)$

$=P(B_1)P(A|B_1)+P(B_2)P(A|B_2)+ \cdots + P(B_n)P(A|B_n)$

- Introductiona)Illustrating the Law of Total Probability for two conditional eventsb)The Law of Total Probability for more than two events
- 1.
**2 disjoint mutually exclusive events**

Back Country skiers can be divided into two classes, those with avalanche training and those who have no avalanche training. An individual with avalanche training has a probability of 0.05 of getting in an avalanche, while an individual without avalanche training has a probability of 0.20 of being in an avalanche. If 75% of backcountry skiers have avalanche training and 25% of back country skiers do not, then what is the probability that a randomly selected backcountry skier will be in an avalanche? - 2.
**3 or more disjoint mutually exclusive events**

I have 3 bags that each contains 5 marbles.

Bag 1:

Bag 2:

Bag 3:

2 Green

4 Green

5 Green

3 Red

1 Red

0 Red

I choose one bag at random and draw a marble. What is the probability that I draw a green marble? - 3.Thomas is frequently late to work. If it is sunny he will be late with probability 0.15; if it rains he is late with probability 0.05. And if it snows he is late with probability 0.5 (if he shows up at all). The meteorologist has predicted there is a 50% it will be sunny tomorrow, a 35% chance it will rain and a 15% chance it will snow. What is the probability that Thomas will be late tomorrow?

Make jokes about taking sick days + make pictures for the sun, rain and snow.