
Let's clarify some vocabulary associated with probability.
These terms can be a bit confusing, so please read carefully.

An experiment is any procedure that can be repeated and has a defined result.

Examples: 
• Experiments: rolling a die, tossing a coin, picking a card from a deck, tossing a coin and spinning a spinner, tossing a coin three times in a row. 


A trial is a repetition of an experiment.

Examples: 
• A die is rolled 20 times and each result recorded. Each individual roll is called a trial within the experiment of all 20 rolls. 


An outcome is a possible result from an experiment. 
Examples: 
• The number 3 is a possible outcome of rolling a die. 


A sample space is the set of all possible outcomes. 
Examples: 
• When rolling a die, the sample space is the set {1, 2, 3, 4, 5, 6}. 


An event is a subset (a portion) of the outcomes in a sample space. 
Examples: 
• An event could be rolling a 5 with a die.
• An event could be rolling a number less than 4 with a die.
• An event could be tossing a head on a penny and rolling a 3 on a die. 


A simple event is an event that consists of a single outcome. There is only one outcome (answer) in the sample space. 
Examples: 
• Probability of rolling a 4 on a die has only one outcome.
• Probability of flipping a coin and getting heads has only one outcome.
• Probability of flipping two coins and getting heads, heads has only one outcome.



A compound event is a combination (union) of two or more simple events. There will be more than one outcome (answer) in the sample space. 
Examples: 
• Probability of rolling a number less than 5 on a die. There are 4 possible answers in the sample space {1, 2, 3, 4}. This is a combination of the four simple events of rolling a 1, rolling a 2, rolling a 3, and rolling a 4 combined.
• Probability of flipping two coins and getting at least one head. There are three possible answers in the sample space {
(H,H), (H,T) (T,H) }. 


Don't confuse "experiment" with "event"!
We think of "events" as big happenings, like the hiphop concert event at the dome. But in probability, the term "event" is less grandiose. The big encompassing word in probability is "experiment". The word "event" is just one act in the experiment.
The "event" is not rolling a die. The "experiment" is rolling a die. The "event" is rolling a 5 on the die. 
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