Probability Formulas

Non-mutually exclusive events

Events that can occur at the same time (have a common outcome)

Mutually Exclusive Events

Events that cannot occur at the same time (don't have a common outcome)

P(A)=1

P(A) certain

P(A)=0

P(A) impossible

Factorial

The result of multiplying all consecutive integers from 1 to the given number. 3!=1x2x3

Choosing a 5 and an even number out of 10

mutually exclusive

Landing a die on 5 and even number

mutually exclusive

Choosing a 7 and and odd number out of 10

non-mutually exclusive

Landing a die on 6 and even number

non-mutually exclusive

Mean

the average, obtained by adding the scores and then dividing by the number of scores

P(A)>P(B)

Event A is more likely than event B

Sample space

A set of all possible outcomes

P(A)<P(B)

Event A is less likely than event B

(Any number from) 0 to 1

Possible probability value

P(A) = The Number Of Ways Event A Can Occur / The total number Of Possible Outcomes

Probability Of An Event

1/10

Probability of choosing a number 3 out of 10

1/5

Probability of choosing number 3 or 5 out of 10

3/5

Probability of choosing number 5 or even number out of 10

1/2

Probability of choosing number 8 or even number out of 10

4/5

Probability of choosing number greater than 4 or even number out of 10

3/5

Probability of choosing number greater than 8 or even number out of 10

P(A or B)= P(A)+P(B)

Probability of mutually exclusive events A and B

P(A or B) = P(A) + P(B)

Probability of mutually exclusive events A and B is the sum of their probabilities

P(A or B)=P(A)+P(B)-P(A and B)

Probability of non-mutually exclusive events A and B

{1, 2, 3, 4, 5, 6}

Sample space in rolled die experiment

{heads, tails}

Sample space in tossed coin experiment

Median

The middle number in a set of numbers that are listed in order

Mode

The number that occurs most often in a set of data