Name: ___________ ______________
Quiz on: ______________
Probability Study Guide
*Probability
-Probability tells us how likely a particular outcome is to occur in a specific situation. The
probability of an outcome for a particular event is a number telling us how likely something
is to happen. This number is the ratio of the number of ways the outcome may occur to
the total number of possible outcomes.
Probability (P) = Number of favorable outcomes
Total number of outcomes
Example: The spinner below is divided into 2 sections, 1 section is black and the other is
white. The Total number of outcomes is 2. The number of chances for the spinner to stop
on black is 1 (because there is only 1 section of the spinner that is black.)
The probability of the spinner landing on
black is 1:2, 1 to 2, one to two, ½.
What is the probability of the spinner landing on black?
Certain –an event is certain to happen only if there is only 1 possible outcome.
Ex: If there are 3 red marbles in a bag, you are certain to pull out a red marble.
Likely –an event is likely to happen if there is a greater chance of one outcome over
another.
Ex: If there are 5 red marbles and 1 blue marble in a bag, you are likely to pull out
a red marble.
Unlikely –an event is unlikely to happen if there is less of a chance a specific outcome will
happen.
Ex: If there are 10 red marbles and 1 blue marble in a bag, you are unlikely to pull
out a blue marble.
Impossible –an event is impossible to happen if there is NO chance of a specific outcome.
Ex: If there are 10 red marbles and 1 blue marble in a bag, it is impossible to pull
out a yellow marble. (There are no yellow marbles in the bag!)
*Help can be found in your textbook on pages 296-297
