11.9 Probability
Probability (chance) is a measure of how likely a certain event will occur.
Proper notation: P(event)
Example: P(H), means the probability of flipping heads in a coin toss
Probability fraction:
favorable outcomes .
total possible outcomes
*When asked to give “probability percent”, simply convert the above fraction to a percent.
Independent Events: the outcome does not depend on another event
Dependent Events: when one event affects another event
Example: taking colored marbles from a bag: as you take each marble there are less marbles left in
the bag, so the probabilities change.
2 or More Events
Find the probability of each separate event and then multiply the events.
Remember to reduce fractions!
Example: (Coin Toss) Find the probability of tossing 3 heads in a row.
1
For each toss of a coin landing on “heads" has a probability of
2
nd
rd
1st toss x 2 toss x 3 toss = probability
1
2
x
1
2
x
1
2
=
1
8