Post on 11-Jan-2016
Probability
• Learning Objective:• To be able to
understand probability and measure the probability of an event not happening
• YOU MUST Be able to know how to work a probability scale
• Some should be able to work out probabilities in different situation
• Some could be able to use experimental probability
The probability scale- RE-Cap from last year
The chance of an event happening can be shown on a probability scale.
impossible certaineven chanceunlikely likely
Less likely More likely
Meeting with King
Henry VIII
A day of the week starting
with a T
The next baby born being a
boy
Getting homework this lesson
A square having four right angles
The probability scale –Re-cap from last year
We measure probability on a scale from 0 to 1.
If an event is impossible or has no probability of occurring then it has a probability of 0.
If an event is certain it has a probability of 1.
This can be shown on the probability scale as:
Probabilities are written as fractions, decimal and, less often, as percentages between 0 and 1.
0 ½ 1impossible certaineven chance
The probability of an event not occurring
The probability of a factory component being faulty is 0.03. What is the probability of a randomly chosen component not being faulty?
P(not faulty) = 1 – 0.03 = 0.97
The probability of pulling a picture card out of a full deck of
cards is .
What is the probability of not pulling out a picture card?
3
13
P(not a picture card) = 1 – =313
1013
Listing possible outcomes
When you roll a fair dice you are equally likely to get one of six possible outcomes:
16
16
16
16
16
16
Since each number on the dice is equally likely the probability of getting any one of the numbers is 1 divided by 6 or .1
6
Calculating probability
What is the probability of the following events?
P(tails) = 12
P(red) = 14
P(7 of ) = 152
P(Friday) = 17
2) This spinner stopping on the red section?
3) Drawing a seven of hearts from a pack of 52 cards?
4) A baby being born on a Friday?
1) A coin landing tails up?
Calculating probability
If the outcomes of an event are equally likely then we can calculate the probability using the formula:
Probability of an event =Number of successful outcomes
Total number of possible outcomes
For example, a bag contains 1 yellow, 3 green, 4 blue and 2 red marbles.
What is the probability of pulling a green marble from the bag without looking?
P(green) =310
or 0.3 or 30%
Calculating probability – IN your books calculate
A fair dice is thrown. What is the probability of gettinga) a 2?b) a multiple of 3?c) an odd number?d) a prime number?e) a number bigger than 6?f) an integer?
d) P(a prime number) = 36
e) P(a number bigger than 6) =
f) P(an integer) = 66
= 1
=12
0
Don’t write 0
6
The probability of an event not occurring
If the probability of an event occurring is p then the probability of it not occurring is 1 – p.If the probability of an event occurring is p then the probability of it not occurring is 1 – p.
The following spinner is spun once:
What is the probability of it landing on the yellow sector?
P(yellow) =14
What is the probability of it not landing on the yellow sector?
P(not yellow) =34
The probability of an event not occurring
The probability of a factory component being faulty is 0.03. What is the probability of a randomly chosen component not being faulty?
P(not faulty) = 1 – 0.03 = 0.97
The probability of pulling a picture card out of a full deck of
cards is .
What is the probability of not pulling out a picture card?
3
13
P(not a picture card) = 1 – =313
1013