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GCSE Revision Guide homepage
This page contains a mix of problems
associated with GCSE probability – including a look at a sample space problem
Two independent events
Two spinners
Suppose you spin two spinners.
Spinner 1 is split into three equal
sections (RED, GREEN and AMBER)
Spinner 2 is split into four equal
sections (TWO RED, GREEN and AMBER)
Suppose you win if the two colours are the same
We can represent the outcomes using a
two-way table
|
|
|
Spinner
2 |
|||
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|
|
Red |
Red |
Green |
Amber |
|
Spinner 1 |
Red |
R,R |
R,R |
R,G |
R,A |
|
Green |
G,R |
G,R |
G,G |
G,A |
|
|
Amber |
A,R |
A,R |
A,G |
A,A |
|
We can count the number of
options/outcomes as 12 (because there are twelve outcomes within the table)
We can see 
Two dice
Suppose you roll two dice and
multiply the numbers to get a score. You win if the answer is a prime number.
We can also represent this in a table
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Dice
2 |
|||||
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|
1 |
2 |
3 |
4 |
5 |
6 |
|
Dice 1 |
1 |
1 |
2 |
3 |
4 |
5 |
6 |
|
2 |
2 |
4 |
6 |
8 |
10 |
12 |
|
|
3 |
3 |
6 |
9 |
12 |
15 |
18 |
|
|
4 |
4 |
8 |
12 |
16 |
20 |
24 |
|
|
5 |
5 |
10 |
15 |
20 |
25 |
30 |
|
|
6 |
6 |
12 |
18 |
24 |
30 |
36 |
|
REMEMBER – ONE IS NOT A PRIME NUMBER!
The number of possible outcomes is 36
The number of prime numbers 6
So 
GIVEN A TABLE OF CONTINUOUS DATA – dependent events
The table below shows the times which
as class of 17 people ran.
|
Running
time |
Frequency |
|
|
2 |
|
|
5 |
|
|
7 |
|
|
3 |
1)
A teacher picks out one person
at random. What is the probability they ran over 14 seconds?
There are 10 people who ran
over 14 seconds so
2)
The teacher picks out two
people. What is the probability they both
ran under 16 seconds
REMEMBER THAT the FRACTION
CHANGES FOR THE SECOND PERSON BECAUSE ONE PERSON HAS ALREADY BEEN PICKED OUT
|
Person
1 Under
16 seconds |
AND |
Person
2 Under
16 seconds |
|
Answer |
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