Probability Flashcards
How do you find the probability of an event when all possible outcomes are equally likely?
Number of outcomes where event happens/Total number of possible outcomes
What is a sample space?
The set of all possible outcomes of a trial.
How do you find the expected frequency of an event?
n*P(A) where n is the number of trials and A is the event.
What must the total probability always add up to?
1
What does P(A’) mean and how would you work it out?
Probability of not A. 1 - P(A)
When looking at a Venn diagram what does ‘given that x’, where x is one of the events, mean?
Out of the circle representing x.
What does a two-way table represent ?
The sample space.
What do the cells represent in a two-way table?
Different events.
What is the addition law?
For two events, A and B: P(A or B) = P(A) + P(B) - P(A and B)
What does it mean if events are mutually exclusive?
They cannot happen at the same time. P(A and B) = 0
For mutually exclusive events A and B, what is P(A or B)?
P(A) + P(B)
How do you show that two events are mutually exclusive?
Show that P(A and B) = 0.
What does it mean if events are independent?
One happening does not affect the other.
For independent events A and B, what is P(A and B)?
P(A)*P(B)
How do you show that events A and B are independent?
Show that P(A)*P(B) = P(A and B).
