Probability

• Mathematics
• Lower Secondary (Key Stage 3)

Probability

Probability is simply how likely something is to happen

How many words can you
find relating to probability

If you got:

1-4

5-8

9-12

13+

you are:

Good

Ace

Awesome

Superstar

Probability is simply how likely something is to happen

Where would you place these words on the probability line

Likely Certain Impossible Unlikely  Evens

Where would you place these percentages on the probability line

100%chance, 75%chance  50%chance, 25%chance, 0% chance.

100% chance

75% chance

50% chance

25% chance

0% chance

likley

evens

certain

Impossible

unlikely

How can we be more accurate when talking about probability?​

We express probability as a number between 0 and 1.​​

The probability for an event which is IMPOSSIBLE is 0.​

The probability for an event which is CERTAIN is 1.​​

Probability can be expressed as a fraction, a decimal or a percentage.​

Think - Pair - Share

Use the words/ numbers to describe the probabilities of these events 

1. You will celebrate your 10th birthday tomorrow.
2. It will rain tomorrow.
3. Everyone will be on time for class.
4. The next person to pass you in the corridor is a female.
5. You will stay up late tonight playing on a computer.
6. You have checked your social media this morning before you got out of bed.
7. The sun will rise tomorrow.
8. It will snow on Christmas day.
9. You will win the lottery on Saturday night.
10. Morocco will win the football world cup 

You will celebrate your 10th birthday tomorrow.
It will rain tomorrow. Everyone will be on time for class.
The next person to pass you in the corridor is a female.
You will stay up late tonight playing on a computer.
You have checked your social media this morning before you got out of bed.
The sun will rise tomorrow. It will snow on Christmas day.
You will win the lottery on Saturday night. Morocco will win the football world cup

 To calculate the probability, when all possible outcomes are equally likely we can use the following formula

 Probability = number of ways an outcome can happen

                            divided by the total number of outcomes

For example I have a bag with   2 pieces of fruit in it 

I pear and 1 apple what are the chances of me picking the pear 

1pear divided by 2 pieces of fruit is

1/2 or 50% 

Probability Example

If i have a bag of sweets, 5 are red, 3 are blue and 2 are yellow. What is the probability that i select a blue sweet at random?

First... how many blue sweets are there?....3

Second .... how many sweets are there in total? .....10

Therefore i have a 3 in 10 chance of picking a blue sweet - 3/10

Probability Example

I roll a normal 6 sided dice. 

What is the probability that i roll a number less than 5?

First... What are my outcomes?.... 1 2 3 4.... 4 outcomes

Second ... what could i roll? .... 1 2 3 4 5 6 ..... 6 outcomes in total

Probability of rolling a number less than 5 = 4 (outcome) / 6 (total) .... We could simplify this to 2/3

What is the probability of snow falling in the month of May in Northern Ireland

1. Impossible
2. Very unlikely
3. Certain
4. Evens

There are 40 cubes in a bag.
Two of them are yellow.​
What is the probability of picking,
at random, a yellow cube?

1. 1/40
2. 2/40
3. 2/38
4. 1/2

This dice has eight sides.​
What is the probability of the
4 landing uppermost?​

1. 1/16
2. 4/8
3. 1/8
4. 2/8

A pack of 52 cards is shuffled.​
What is the probability of
selecting, at random,
the ace of spades?

1. 1/13
2. 4/52
3. 1/52
4. 1/4

Two coins are tossed.​
What is the probability of
them landing both tails?​

1. 1/4
2. 2/4
3. 1/3
4. 4/4

A pack of 52 cards is shuffled.​
What is the probability of
selecting, at random,
any ace of ?

1. 4/13
2. 4/52
3. 1/52
4. 1/4

When throwing two dice,
what is the probability
of scoring a double six?

1. 1/36
2. 1/12
3. 2/36
4. 2/12

There are 200 straws in this
packet, coloured pink, orange,
green and yellow. What is the
probability of picking at random
a blue one?

1. 0
2. 1/200
3. 1/4
4. 1/100

There are 200 straws in this
packet, coloured pink, orange,
green and yellow. What is the
probability of picking at random
a red one?

1. 0.1
2. 0.2
3. 0.25
4. 0

This bingo machine has 90 balls,
from 1 – 90.​What is the probability
of the number on a ball ending
in zero?

1. 0.0
2. 1/90
3. 1/9
4. 10%

This dice is loaded.
The probability of it
landing on a one is 0.8​
What is the probability of it
not landing on a one?

1. 5/6
2. 1/6
3. 0.4
4. 0.2

Sean makes a fair
6 sided spinner
what is the chance
that the spinner land on a 3

1. O.1
2. 0.3
3. 0.5
4. 0.6

Sean has a box of pens. The box contains 6 blue pens,
8 black pens and 3 red pens.
What is the probability that he will pick a blue pen?

1. 1/17
2. 6/8
3. 6/11
4. 6/17

Some more blue pens are added to the box.
The probability of selecting a blue pen is now ½
How many blue pens were added to the box?

1. 7
2. 5
3. 11
4. 2