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

Class work

• Framworking 3- Exercise 3b 1-7