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SOL 3.18 Probability and Statistics
NOTEPAGE FOR STUDENT
Page 1
Probability
What is the chance, or probability that it will snow tomorrow? That is a question all
school children and their teachers ask in the winter months!
Probability tells the chance an event will happen. We describe all the
possible outcomes or ways something might happen by using these words:
impossible, unlikely, equally likely, likely, and certain.
We can describe some events using these words.

My dog singing songs is impossible.

Snow in the Sahara Desert is unlikely.

Tossing a coin and it landing heads up is equally likely or as likely as it landing tails up.

The school bus picking me up for school is likely.

The sun rising tomorrow is certain.
We can think of all these outcomes along a line going from impossible to certain with
equally likely in the middle.
Impossible
Unlikely
Equally likely
Likely
Certain
Think! What are some outcomes that would be certain to happen?
Think! What are some outcomes that would be impossible to happen?
Think! What are some outcomes that would be equally likely to happen?
If all the outcomes of an event are equally likely to occur, the probability of the event happening
is:
Event = number of favorable outcomes
total number of possible outcomes
©2011
SOL 3.18 Probability and Statistics
NOTEPAGE FOR STUDENT
Page 2
Probability
All possible outcomes for an experiment is called the sample space.
Toni had three pairs of pink mittens and one pair of black mittens. She kept them in her dresser
drawer. If she reaches in on a dark morning and doesn’t look carefully, which color mitten is she
most likely going to pick?
Sample Space: pink or black
Probability of Pink Mitten =
When we do experiments in probability, we can use things like number cubes or dice, coins
or plastic chips, or even spinners we might use in a board game.
However, one of the easiest ways to show how probability works is to toss a coin, like a penny.
What is the chance that the coin will land heads up?
It only has two possibilities: heads or tails. The probability that heads will occur is one or
the other. Both outcomes are equally likely. We are just as likely to roll heads as we are to roll
tails.
Sample
Space:
heads
Sample
Space:
headsor
ortails
tails
OR
©2011
Probability of Heads =
1
2
Probability of Tails =
1
2
SOL 3.18 Probability and Statistics
NOTEPAGE FOR STUDENT
Page 3
Probability
PRACTICE!
1. Let’s take the penny to another level. How many times would the penny land heads up if
we tossed it 10 times? Try it and record what happens.
Another way to test probability is to use a number cube. When we roll a cube, we can roll the
numbers 1, 2, 3, 4, 5, or 6.
2. What is the chance that we would roll a number less than 7?

Impossible

Likely

Unlikely

Certain
3. What is the chance we would roll a 7?

Impossible

Likely

Unlikely

Certain
Sample Space:
1
4
2
5
3
6
We can also test probability using a game spinner. The spinner could land on either the striped,
green, or yellow sections.
4. What is the chance the arrow would land on a striped section?

Equally likely

Likely

Unlikely

Certain
Sample Space:
Striped
Green
Yellow
Probability of
striped section
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