Probability Vocabulary
Certain probability
 Sure to happen; having a probability of 1
combination
 An arrangement of items or events in which
order does not matter.
 Ex: For objects A, B, C and D, there are 6
different combinations of 2 objects:
AB, AC, AD, BC, BD, CD
Compound event
 An event made up of two or more simple
events.
 Ex: rolling a 3 on a number cube and spinning
a 2 on a spinner is a compound event.
Dependent events
 Events for which the outcome of one event
affects the probability of the second event.
 EX: A bag contains 3 red marbles and 2 blue
marbles. Drawing a red marbles and then
drawing a blue marble without replacing the
first marble is an example of dependent
events.
Equally likely
 Outcomes that have the same probability
Event
 An outcome or set of outcomes of an
experiment or situation
 EX: when rolling a number cube, the event
“an odd number” consists of the outcomes 1,
3, and 5.
experiment
 In probability, any activity based on chance,
such as tossing a coin.
Experimental probability
 The ratio of the number of times an event
occurs to the total number of trials, or times
that the activity is performed.
 EX: Kendra attempted 27 free throws and made 16 of
them. Her experimental probability of making a free
throw is:
number made
= 16
number attempted
27
Fair
 When all outcomes of an experiment are
equally likely, the experiment is said to be fair.
Impossible (probability)
 Can never happen; having a probability of 0.
Independent Events
 Events for which the outcome of one event does not
affect the probability of the other.
 Example: A bag contains 3 red marbles and 2 blue
marbles. Drawing a red marble, replacing it, and then
drawing a blue marble is an example of independent
events.
Outcome
 A possible result of a probability experiment.
 Example: When rolling a number cube, the
possible outcomes are 1,2,3,4,5, and 6.
Prediction
 Something you can reasonably expect to happen in
the future.
Probability
 A number from 0 to 1 (or 0% to 100%) that
describes hoe likely an event is to occur.
 Example: A bag contains 3 red marbles and 4
blue marbles. The probability of randomly
choosing a red marble is 3/7.
Random Sample
 A sample in which each individual or object in
the entire population has an equal chance of
being selected.
 Example: Mr. Henson chose a random sample
of the class by writing each student’s name
on a slip of paper, mixing up the slips, and
drawing five slips without looking.
Sample Space
 All possible outcomes of an experiment.
 Examples: When rolling a number cube, the
sample space is 1,2,3,4,5,6.
Simple Event
 An event consisting of only one outcome.
 Example: In the experiment of rolling a
number cube, the event consisting of the
outcome 3 is a simple event.
Theoretical Probability
 The ratio of the number of ways an event can
occur to the total number of equally likely
outcomes.
 Examples: When rolling a number cube, the
theoretical probability of rolling a 4 is 1/6.
Trial
 Each repetition or observation of an
experiment.
 Example: When rolling a number cube, each
roll is one trial.