Probability Flashcards
Probability
number of ways to get desired outcome / total possible outcomes
Compound Events
a combination of simple events (ie: rolling two dice or flipping a coin three times)
Permutations: How many different ways can we arrange x items out of n in which order matters?
If no repetition is allowed, use: n! / (n-k)! If repetition is allowed, used: n^x
Combinations: How many ways are there to arrange x items out of n in which order does NOTmatter?
n! / (n-x)!x!
In how many unique orders can 5 horses finish a race? (hint: combination because order does not matter)
5! 5x4x3x2x1
Look for permutations anytime order…
matters
Look for combinations anytime order…
does not matter
Enumeration
writing it out
Factorial
n! n x n-1 x n-2…
Conditional Probability of disjoint independent events (ie: rolling an odd number or a 4 on one die)
P(A or B) = P(A) + P(B)
Conditional Probability of non-disjoint independent events (ie: choosing a spade or a jack)
P(A or B) = P(A) + P(B) - P (A and B) subtract the overlap
Complement (of any event, A)
The probability of A not happening
If two events are DISJOInT ie: rolling an odd number or a 4 on one die?
Add the two events Ie: 1/2 + 1/6
Joint Probability
The probability of the intersection of two events (probability that both events occur)
Independent events
The probability of one is not affected by whether the other event occurred