I DO KNOW MR.PITT HAS ALREADY DONE A PROBABILITY PAGE!


Probability is demonstrated with a fraction, for example:
There are 10 marbles in a bag, 5 are black, 2 are white, 1 is each blue and red.
What is the probability of picking a black marble at random?
Answer: Obviously external image gif.latex?%5Cinline%20%5Cfrac%7B1%7D%7B2%7D


Now a harder question:

What is the probability of choosing a black marble, putting it back, then choosing a red?

Answer: You would do external image gif.latex?%5Cinline%20%5Cfrac%7B1%7D%7B2%7D%20X%20%5Cfrac%7B1%7D%7B10%7D, which makes external image gif.latex?%5Cinline%20%5Cfrac%7B1%7D%7B20%7D



Even Harder:

What is the probability of choosing a black without putting it back, and then choosing a blue?

Answer: Do external image gif.latex?%5Cinline%20%5Cfrac%7B1%7D%7B2%7D%20X%20%5Cfrac%7B1%7D%7B9%7D%20=%20%5Cfrac%7B1%7D%7B18%7D

Tree Diagrams:

FIRST
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A tree diagram of a coin being tossed 3 times looks like this:
image: tree diagram and probabilities
image: tree diagram and probabilities

The probability of three heads is:
P (H H H) = 1/2 × 1/2 × 1/2 = 1/8
P (2 Heads and a Tail) = P (H H T) + P (H T H) + P (T H H)
= 1/2 × 1/2 × 1/2 + 1/2 × 1/2 × 1/2 + 1/2 × 1/2 × 1/2
= 1/8 + 1/8 + 1/8
= 3/8


Question:
image: tree diagram with missing probabilities
image: tree diagram with missing probabilities

Fill in the missing probabilites


Answer:
image: tree diagram with probabilities
image: tree diagram with probabilities


Ed Walden 8J
Feel free to add or change anything if you think (or is) wrong


Still don't get it? Ask Mr. Pitt!