CHAPTER 6

Question 1

what is probability?

Answer 1

• a numerical measure of the chance of an event happening

Question 2

what does it mean if a probability is 0?

Answer 2

• impossible for the event to happen

Question 3

what does it mean if a probability is 1?

Answer 3

• the event is certain to happen

Question 4

how can you write probabilities?

Answer 4

• as fractions
• as decimals
• as percentages

Question 5

probability of an event equation:

Answer 5

probability of an event= number of successful outcomes/ total number of possible outcomes

Question 6

expected frequency equation:

Answer 6

expected frequency of an event A= P(A) x number of trials

Question 7

what is the expected frequency?

Answer 7

• the number of times you expect the event to happen
• it is not necessarily what actually will happen

Question 8

what is a trial?

Answer 8

• each experiment (or response to a survey)

Question 9

estimated probability equation:

Answer 9

estimated probability= number of trials with successful outcome/ total number of trials

Question 10

risk of an event equation:

Answer 10

risk of event= number of trials in which event happens/ total number of trials

Question 11

what is the absolute risk?

Answer 11

• the probability of an event happening

Question 12

what is the relative risk?

Answer 12

• how many times more likely an event is to happen for one group compared to another group

Question 13

relative risk for a group equation?

Answer 13

risk for those in the group/ risk for those not in the group

Question 14

what is a list of all the possible outcomes called?

Answer 14

• sample space (S)

Question 15

what conditions must be met for a sample space diagram?

Answer 15

• the outcomes must be equally likely
• can use if there are two events

Question 16

what does each region of a probability Venn diagram represent?

Answer 16

• The probability of a different outcome

Question 17

what should the sum of probabilities represented in a Venn diagram be?

Answer 17

must equal 1

Question 18

when are events mutually exclusive?

Answer 18

• they cannot happen at the same time

Question 19

addition law for two mutually exclusive events:

Answer 19

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

Question 20

when is a set of events exhaustive?

Answer 20

• if the set contains all possible outcomes

Question 21

when is the sum of all the probabilities 1?

Answer 21

• for a set of mutually exclusive, exhaustive events, the sum of all of the probabilities is equal to 1

Question 22

how do you write the probability of an event not happening?

Answer 22

P(not A)

Question 23

how to work out P(A):

Answer 23

P(A) + P(not A)= 1

Question 24

how to work out P(not A):

Answer 24

P(not A)= 1- P(A)

Question 25

general addition law for events which are not mutually exclusive:

Answer 25

- P(A U B)= P(A) + P(B)- P(A intersection B)

Question 26

what does each branch of a tree diagram represent?

Answer 26

- an outcome - the probability of the outcome is written on the branch

Question 27

when are two events conditional?

Answer 27

- if the outcome of one event affects the outcome of the other event - conditional events are not independent

Question 28

conditional probability:

Answer 28

- the probability that B will happen if A has happened the conditional probability if B given A - it is written P(B|A)

Question 29

formula for conditional probability of B given A:

Answer 29

P(B|A)= P(A and B)/ P(A)

Question 30

formula for the probability of A and B:

Answer 30

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

Question 31

formula for testing if two events are independent:

Answer 31

P(A)= P(A|B) - if P(A) and P(A|B) are not equal the events are not independent (they are conditional)