PROBABILITY
Lesson 1
Probability

Is a number that shows how likely it is
that an event will happen

You might also hear it called chance.

Can be expressed as fractions, decimals
or percentages, or on a probability scale.
Probability

We can look at a scale of chance to see
how likely it is that something will happen

If something has a low probability, it is
unlikely to happen.

If something has a high probability, it is
likely to happen.
0
Chance
impossible
½
Even Chance
1
Certainty
The Language of Probability
Any number less than 1 or greater
than 6.
White, because there are more
white marbles than any other
colour.
Outcomes and Tree Diagrams
Lesson 2
How to Record Probability
Probability is recorded as a fraction,
decimal or percent
 To record it as a fraction:

P(event) =
Number of favourable outcomes
Total number of possible outcomes
An outcome is the possible result of an
event or an experiment
 When a coin is tossed, the possible
outcomes are heads or tails

HOW to Calculate Probability
Figure out the denominator first (total
number of outcomes)
2. Figure out the numerator (the
favourable outcome, which is what you
want)
Example. If I have a die, what is the
probability I get an odd number?
1.

Sometimes, it is not so easy to figure out
the total number of outcomes. In that
case, we need a strategy...

Sometimes, it is not so easy to figure out
the total number of outcomes. In that
case, we need a strategy...
Lists or Tree diagrams
Tree Diagrams
Line everything up into columns
 1 column for each event, with columns
branching off the ones before them
 End with an outcomes column (made by
reading across tree branches)

Example:
Eli spins the pointer on this spinner and rolls a
number cube labelled 1 to 6
You must draw the tree diagram to represent
the situation
a)
How many outcomes include rolling an odd
number and spinning red?
Theoretical Probability
Theoretical probability is the likelihood of
an event happening based on all the
possible outcomes (calculated)
Task 1
The Scenic Railroad sells tickets for trips on
Saturdays and Sundays. All-day and half-day
trips are available. There are adult, child, and
senior fares. Draw a tree diagram to show the
possible ticket types.
Task 2

Complete Investigating Probability 6.2.2
Experimental Probability

Experimental Probability is a measure of likelihood of an event
based on data from an experiment and is written in the form
P(event) =

Number of times desired outcome occurs
Total number of trials in the experiment
When conducting a probability experiment, create a table
so that you can tally your results.