April 13, 2023

Probability

1. Probability of an event not happening

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April 13, 2023ReviseProbabilities can be expressed as fractions, decimals or percentages.

All probabilities lie on a scale of 0 to 1, or 0% to 100%.

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Rolling a die, or any single occurrence for which we can calculate the probability, is known as an event.

Every event has an outcome, in this case, rolling the number five is the outcome.

The sum of the probability of all events happening is 1.

April 13, 2023

Some things are more likely to happen than others.You would be more likely to roll a five with a fair die,than win the national lottery jackpot with a single ticket.

There are 6 equally likely outcomes when you roll a die.16

The probability of rolling any one of these numbers is

There are 13,983,818 possible number combinations in the national lottery draw.The probability of having the winning ticket is 1

13,983,818

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Explanation

April 13, 2023

PThe probability that a particular outcome will happen can be written in the shorthand (outcome)

P(rolling a 5) = 16

Asking the probability of not rolling a 5, is the same as asking the probability of rolling a 1 or 2 or 3 or 4 or 6.

P(not rolling a 5) = 56

or 1 – 16

so

The probability of an event not happening = 1– P

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Explanation

April 13, 2023

There are 52 cards in a pack, in four suits, hearts, clubs, diamonds and spades.What is the probability of dealing out the 10 of spades?

P = 1

52

The card is replaced and the pack shuffled.

P = 1

521 – =5152

What is theprobability of dealing out a card that is not the 10 of spades?

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Example

April 13, 2023

The queen is replaced and the pack shuffled again.What is the probability of not dealing a club?

52 ÷ 4 = 13

P(dealing a club) =1352 =

14

P(not dealing a club) = 1 – 14

= 34

There are 52 cards and 4 suits

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Example

April 13, 2023

P(taking a bus to school) =

Mikel decides to take a bus to school three days a week, in an average week.What is the probability that he did not do so today?

The weather centre forecasts that there is a 60% chance of it raining tomorrow.What is the probability that it will not rain?

100% – 60% = 40%

35

1 – P = 25

Examples

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