Probability
·
Probabilities
are written as fractions or decimals, and less often as percentages
·
An
event can have several possible outcomes
·
Each
outcome has a probability or chance of occurring
·
When
a fair dice is thrown there is equal chance of throwing each number. The outcomes from the event throwing a dice
are equally likely outcomes
·
If
the outcomes of an event are equally likely, the probability can be calculated
using:
Probability
of an event = number of successful outcomes
Total
number of possible outcomes
MUTUALLY EXCLUSIVE EVENTS
·
Outcomes
that cannot happen at the same time are called mutually exclusive outcomes
·
E.g.
A dice is rolled. It shows 5. It is rolled again. It shows 2. These events cannot happen at the same time. They are mutually exclusive
·
The
total probability of mutually exclusive outcomes is 1. An event cannot happen and not happen at the
same time
·
The
sum of the probabilities of mutually exclusive outcomes is 1
·
Probability
of rolling a 5
= 1 – Probability of NOT
rolling a 5.
THE “OR” RULE
·
If
two events, A and B are mutually exclusive:
·
P(A
or B) = P(A) + P(B)
· This
is known as the “OR” rule or addition rule for mutually exclusive
probabilities.
INDEPENDENT EVENT
ü
Two
events are independent when the probability of one event happening is not
affected by the outcome of the other event
ü E.g. Roll a dice and flip a coin.
Event
A: the dice shows an odd number
Event
B: the coin shows tails.
These
events are independent. Neither outcome
can influence the other.
ü Are
these events independent?
You go
outside. Event A: It is snowing Event B: It is cold
THE “AND” RULE
§ To
find the probability of two independent events both happening, multiply the
individual probabilities together
§ If
A and B are individual events
P(A
and B) = P(A) x P(B)
This
is the AND rule or multiplication rule.
E.g. The probability of rolling an odd number on a
dice AND flipping a coin to get tails is:
No comments:
Post a Comment