 # Simple Probability

In this worksheet, students work out the probability of an event happening. Key stage:  KS 2

Curriculum topic:   Maths and Numerical Reasoning

Curriculum subtopic:   Probability

Difficulty level:   ### QUESTION 1 of 10

Probabilities are written as FRACTIONS.

On the top of the fraction, we put the number of ways there are of your event happening.

On the bottom of the fraction, we put the total number of possible outcomes.

Reduce the fraction if you can.

Example

There are 3 red balls and 5 blue balls in a bag.

What is the probability of choosing a red ball?

On the top of the fraction, we put the number of ways there are of your event happening.  This will be the number of red balls (i.e. 3)

On the bottom of the fraction, we put the total number of possible outcomes.  This will be the total number of balls (3 + 5 = 8)

The probability is 3/8

O   O   O        O   O   O   O   O   O    O

There are 3 red balls and 7 blue balls in a bag.

What is the probability of choosing a red ball when you select one at random?

0

3/7

3/10

7/10

O   O   O        O   O   O   O   O   O    O

There are 3 red balls and 7 blue balls in a bag.

What is the probability of choosing a green ball when you select one at random?

0

3/7

3/10

7/10

O   O         O   O   O   O   O   O    O

There are 2 red balls and 7 blue balls in a bag.

What is the probability of choosing a blue ball when you select one at random?

0

2/9

2/7

7/9

O   O         O   O   O   O   O

There are 2 red balls and 5 blue balls in a bag.

What is the probability of choosing a blue ball when you select one at random?

1

5/7

2/7

2/5

O   O   O   O   O         O   O   O   O   O

There are 5 red balls and 5 blue balls in a bag.

What is the probability of choosing a red ball when you select one at random?  Simplify your answer as far as possible

1

5/5

1/2

5/10

O   O             O   O   O   O

There are 2 red balls and 4 blue balls in a bag.

What is the probability of choosing a red ball when you select one at random?

1

1/3

1/2

2/4

O   O             O   O   O   O

There are 2 red balls and 4 blue balls in a bag.

What is the probability of choosing a blue ball when you select one at random?

1

1/3

1/2

2/3

O   O   O             O   O   O   O

There are 3 red balls and 4 blue balls in a bag.

What is the probability of choosing a blue ball when you select one at random?

4/7

4/3

3/4

2/3

Which of these cannot be probabilities? (Select more than one answer)

0

4/3

3/4

8/7

There are 54 red balls in a bag and 37 blue balls in a bag.

What is the probability of choosing a white ball when one is selected at random?

• Question 1

O   O   O        O   O   O   O   O   O    O

There are 3 red balls and 7 blue balls in a bag.

What is the probability of choosing a red ball when you select one at random?

3/10
EDDIE SAYS
There are 3 red balls There are 10 balls in total
• Question 2

O   O   O        O   O   O   O   O   O    O

There are 3 red balls and 7 blue balls in a bag.

What is the probability of choosing a green ball when you select one at random?

0
EDDIE SAYS
There are 0 green balls There are 10 balls in total
• Question 3

O   O         O   O   O   O   O   O    O

There are 2 red balls and 7 blue balls in a bag.

What is the probability of choosing a blue ball when you select one at random?

7/9
EDDIE SAYS
There are 7 blue balls There are 9 balls in total
• Question 4

O   O         O   O   O   O   O

There are 2 red balls and 5 blue balls in a bag.

What is the probability of choosing a blue ball when you select one at random?

5/7
EDDIE SAYS
There are 5 blue balls There are 7 balls in total
• Question 5

O   O   O   O   O         O   O   O   O   O

There are 5 red balls and 5 blue balls in a bag.

What is the probability of choosing a red ball when you select one at random?  Simplify your answer as far as possible

1/2
EDDIE SAYS
There are 5 red balls There are 10 balls in total
• Question 6

O   O             O   O   O   O

There are 2 red balls and 4 blue balls in a bag.

What is the probability of choosing a red ball when you select one at random?

1/3
EDDIE SAYS
There are 2 red balls There are 6 balls in total
• Question 7

O   O             O   O   O   O

There are 2 red balls and 4 blue balls in a bag.

What is the probability of choosing a blue ball when you select one at random?

2/3
EDDIE SAYS
There are 4 blue balls There are 6 balls in total
• Question 8

O   O   O             O   O   O   O

There are 3 red balls and 4 blue balls in a bag.

What is the probability of choosing a blue ball when you select one at random?

4/7
EDDIE SAYS
There are 4 blue balls There are 7 balls in total
• Question 9

Which of these cannot be probabilities? (Select more than one answer)

4/3
8/7
EDDIE SAYS
On the top of the fraction, we put the number of ways there are of your event happening. On the bottom of the fraction, we put the total number of possible outcomes.
The bottom number has to be higher than the top number to describe a probability.
• Question 10

There are 54 red balls in a bag and 37 blue balls in a bag.

What is the probability of choosing a white ball when one is selected at random?

0
EDDIE SAYS
There are no white balls in the bag
---- OR ----

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