Probability Key Formulae and Key Terms

Question 1

What is the set of all possible outcomes from an event?

Answer 1

Sample/Probability Space.

Question 1

What is P(event)?

Answer 1

No of ways event can happen / no of possible ways

Question 2

What is P(4) when throwing an unbiased dice?

Answer 2

1/6

Question 3

What is the rule for probability values?

Answer 3

They are between 0 and 1.

Question 4

If P(A) = x, what is P(not A)?

Answer 4

1-x

Question 5

When drawing a venn diagram, what do you have to draw to receive full marks?

Answer 5

A box around all circles and values.

Question 6

What does P(AnB) represent?

Answer 6

The intersection between A and B, i.e. when both A and B occur.

Question 7

What does P(AuB) represent?

Answer 7

All values that are either A or B, including the intersection.

Question 8

What does P(A’nB’) represent?

Answer 8

All values neither A nor B nor both.

Question 9

When drawing a triple venn diagram, what value should you fill in first?

Answer 9

The intersection of all 3.

Question 10

If two events are mutually exclusive, what are they?

Answer 10

They cannot occur together.

Question 11

If you were to draw a venn diagram of A and B and they were mutually exclusive, what would this look like?

Answer 11

A box with two circles containing no intersection between them.

Question 12

If A and B are mutually exclusive, what is P(AuB) equal to?

Answer 12

P(A) + P(B)

Question 13

If A and B are mutually exclusive, what is P(AnB) equal to?

Answer 13

0

Question 14

What is the ‘forgotten’ formula for non-mutually exclusive events?

Answer 14

P(A) + P(B) - P(AnB)

Question 15

What does P(A|B) represent?

Answer 15

P(A) given that B has occured.

Question 16

What is P(A|B) equal to?

Answer 16

P(AnB) / P(B) or P(intersection) / P(B)

Question 17

If two events are independent, what are they?

Answer 17

Events that do not influence the likelihood of the other.

Question 18

Providing A and B are independent, what is P(AnB) equal to?

Answer 18

P(A) x P(B)

Question 19

What are the three formulae for mutually exclusive events?

Answer 19

P(AuB) = P(A) + P(B)
P(AnB) = 0
P(A|B) = 0

Question 20

What are the two formulae for independent events?

Answer 20

P(Anb) = P(A) x P(B)
P(A|B) = P(A)

Question 21

What formulae are there aside from mutually exclusive and independent events?

Answer 21

P(AuB) = P(A) + P(B) - P(AnB)
P(A|B) = P(AnB) / P(B)

P(at least one) = 1 - P(none)
P(at least two) = 1 - [ P(0) + P(1) ]