Download Probability

Probability
Understand the vocabulary and ideas
of probability.
Understand and use a probability
scale.
Probability Vocabulary
Put these words in order of likeliness
Equally likely
Probability Vocabulary
We put the words on a probability scale
Impossible
Equally likely
Unlikely
Likely
Certain
Where would you place these
statements on a probability scale?
Impossible
Certain
A coin lands Heads side up
Next year will have 54 Fridays
The day after Monday will be Tuesday
You will watch TV tonight
It will rain in London in the first week of July
A new born baby will be a girl
What about these events?
Impossible
Certain
You will be injured next time you play in a sports game
A road accident will occur if the road is icy
A road accident will occur in normal driving conditions
A cyclone will occur in England
A man will die before the age of 70
Rather than using words we use
numbers on the probability scale
Impossible
0
Certain
0.5
1
The probability of an event occurring is written
as a fraction, a decimal or a percentage, e.g.
The probability of getting an even number on
rolling a dice is ½ or 0.5 or 50%
How likely?
• To find the probability of an event occurring,
work out how many things (called outcomes)
could happen.
• Count how many of them give you the
required event
• Write these numbers as a fraction:
Number of ways it happens
Number of things that can happen
How likely?
Number of ways it happens
Number of things that can happen
The probability of getting an even number when a dice is rolled:
P(even number) = 3
6
(or ½ or 50% or 0.5)
The probability of selecting a diamond from a standard pack of cards:
P(diamond) = 13
52
(or ¼ or 25% or 0.25)
What’s the probability of …
•
•
•
•
getting a 6 on a dice
a letter chosen from the word RABBIT is a B
getting a number less than 3 on a dice
a pupil picked at random from the class is in
your tutor group
• a person’s birthday is on a Sunday this year
Rolling a fair 6 sided die
On a probability scale mark the probability of
rolling:
A. a 5
B. an odd number
C. a prime number
D. zero
E. a number between 0 and 7
F. a number greater than 2
D
A
BC
F
E
Newspapers
• A newsagent delivers these papers – one to
each house:
• Sun
250
Times
120
• Mirror
300
Mail
100
• Telegraph
150
Express
80
What is the probability that a house picked at
random has:
120/1000 = 0.12
The Times?
The Mail or the Express? (100+80)/1000 = 0.18
Neither the Sun nor the Mirror? (1000-250-300)/1000 =
0.45
Roulette
ODD
6
1
7
2
0
2
6
2
3
1
1
2
1
6
5
4
1
9
2
2
1
4
2
8
8
2
9
1
1
1
0
3
0
2
9
7
2
1
3
2
5
2
4
1
3
1
5
1
8
2
7
EVEN
1
11
21
2
12
22
3
13
23
4
14
24
5
15
25
6
16
26
7
17
27
8
18
28
9
19
29
10
20
30
1 to 10
11 to 20
21 to 30
RED
BLACK
P(odd number) = 15/30 = ½ or 50%
P(1 to 10)
= 10/30 = 1/3 or 33%
P(Black)
= 15/30 = ½ or 50%
P(number 1)
= 1/30 or 3.3%