1. WHAT IS PROBABILITY?

2. LESSON OBJECTIVES Understand and use a probability scale
Interpret statements about probability
Calculate probabilities for single events

3. Understand and use a probability scale
We can measure the chance or likelihood of something happening by using a probability scale.
impossible
even chance
certain
0.5 1 0%
100%
unlikely
50%
likely
Some things probably won’t happen…but they just might. They are unlikely.
Some things are just as likely to happen as to not happen…they are even chance or 50:50.
Some things probably will happen…but they might not. They are likely.
Some things will definitely happen…they are certain.
Some things will never happen…they are impossible.
MyMaths Task

4. What do you think about the following statements?
Interpret statements about probability
Placing the statements on the probability scale shows that we have been interpreting the statements.
What do you think about the following statements?
Is this statement sensible?
Daniel says: “There is a chance that the next person to walk through the door of a supermarket will be someone I know because I will either know them or I won’t.”
Is this statement sensible?
Clare says: “If I buy a lottery ticket every week, I am bound to win sometime.”

5. In your exercise books, complete Exercise 9A.
Now it’s your turn…
In your exercise books, complete Exercise 9A.

6. 1 2 3 There are ten balls in a bag 3 red, 2 blue, and 5 green.
Calculate probabilities for single events
There are ten balls in a bag 3 red, 2 blue, and 5 green.
a. Which colour is most likely to be picked? Why?
b. Which colour is least likely to be picked? Why?
2. In a class of 13 boys and 15 girls, one child is chosen (at random) each day to take the register to the office.
a. Is the child more likely to be a boy or a girl?
b. On a Tuesday, 2 girls are absent. Is a girl more, less or evenly likely to be chosen on this day?
3. To play a game you spin the pointer below: 1 2 3
Which score is least likely?
b. Which score has an even chance of occurring?

7. What is the probability of rolling: 5? b. an odd number?
Calculate probabilities for single events
Are all the possible outcomes equally as likely?
What are all the possible outcomes when rolling a normal and fair dice?
If the probability of rolling a 6 is
What is the probability of not rolling a 6?
What is the probability of rolling:
5? b. an odd number?
zero? d. a number greater than 2?
e. a prime number? f. a number between 0 and 7?