Back to Module 1 notes
Probability: is a number between 0
and 1 (fraction) that tells how likely it is that an event will take
The closer to 1 the more likely it is that the event will occur.
A probability of one, means that the event will always occur.
A probability of zero, means that the event will never occur.
Outcomes are equally likely if they have the same chance of occurring.
Event: What outcome you are testing.
Outcome: What actually happens.
Example, in a bag of colored marbles, the event would be the likelihood of picking a particular color.
If there were 3 red, 4 blue and 3 green marbles, what is the likelihood of picking a red marble?
Experimental probability: When you actually do the event (toss a coin) and count up the actual outcomes. Example: I toss a coin 50 times and 29 out of 50 land on heads.
Theoretical probability: You donít actually do the experiment. Count up how many possible positive outcomes there can be over how many actual outcomes there are.
Example 1: On a fair coin there is
one head, and one tail. That means there is a total of 2 possible
outcomes. The probability of getting a head is 1 out of 2 or
Example 3: If there were 3 red, 4
blue and 3 green marbles, what is the P(red or blue)? Notice how we
wrote this probability question. It means what is the probability of
picking a red or a blue marble. Since there are 3 red marbles and 4 blue
marbles there are 7 possible positive outcomes out of 10 total possible
outcomes so the P(red or blue) is