PROBABILITY
6-4
VOCABULARY
– possible results of an action.
 Event – any outcome or group of outcomes. The
outcomes are called “favorable outcomes”
 Probability – equally likely outcomes. Could be
expressed in a ratio
 Outcomes
Probability
 P(event)
= number of favorable outcomes
number of possible outcomes
Ex.) Find P(rolling an even number) with one
number cube.
# of favorable outcomes = 3
# of possible outcomes 6
P(rolling an even number) = 3/6 or 1/2
Range of Probability
 All
probabilities range from 0 to 1. Most possible
answers will be in fraction or decimal form.
Probability
Less likely
0
IMPOSSIBLE
EVENT
More likely
0.5
Equally likely as
unlikely
1
CERTAIN EVENT
COMPLEMENTS
A
complement of an event is the opposite of that
event. The events “rain” and “no rain” are
complements of each other, for example. The
probability of an event plus the probability of its
complement always equal 1.
EXAMPLE
Find each probability of one roll of a number cube.