# Probability Understand the vocabulary and ideas of probability. Understand and use a probability scale.

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Probability Understand the vocabulary and ideas of probability. Understand and use a probability scale.

Probability Vocabulary Put these words in order of likeliness Impossible Equally likely Unlikely Likely Certain

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? A coin lands Heads side up The day after Monday will be Tuesday Impossible Certain Next year will have 54 Fridays It will rain in London in the first week of July You will watch TV tonight A new born baby will be a girl

What about these events? You will be injured next time you play in a sports game A road accident will occur in normal driving conditions Impossible Certain A road accident will occur if the road is icy A man will die before the age of 70 A cyclone will occur in England

Rather than using words we use numbers on the probability scale Impossible Certain 0 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 DABC FE

Newspapers A newsagent delivers these papers – one to each house: Sun 250Times120 Mirror 300Mail 100 Telegraph 150Express 80 What is the probability that a house picked at random has: The Times? The Mail or the Express? Neither the Sun nor the Mirror? 120/1000 = 0.12 (100+80)/1000 = 0.18 (1000-250-300)/1000 = 0.45

Roulette 2626 2323 1 1616 2020 6 1212 1717 1919 1414 2828 1010 3030 9 7 2121 3 2525 2424 1313 1515 1818 2727 2 1 2929 8 2 4 5 ODD EVEN 11121 21222 31323 41424 51525 61626 71727 81828 91929 102030 1 to 1011 to 2021 to 30 RED BLACK P(odd number) P(1 to 10) P(Black) P(number 1) = 15/30 = ½ or 50% = 10/30 = 1/3 or 33% = 15/30 = ½ or 50% = 1/30 or 3.3%

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