Answer:
5 Probability
5.1 Probabilities
Probabilities are used to describe how likely or unlikely it is that something will happen.
Weather forecasters often talk about how likely it is to rain, or perhaps snow, in particular
parts of the country.
Worked Example 1
(a) When you roll a dice, which number are you most likely to get?
(b) If you rolled a dice 600 times how my sixes would you expect to get?
(c) Would you expect to get the same number of ones?
Solution
(a) You are equally likely to get any of the six numbers.
(b) You would expect to get a six in about 1
6
of the throws, so 100 sixes.
(c) Yes, in fact you would expect to get about 100 of each number.
Worked Example 2
Use one of the following to describe each one of the statements (a) to (d).
Certain
Very likely
Likely
Unlikely
Very unlikely
Impossible
(a) It will snow tomorrow.
(b) It will rain tomorrow.
(c) You win a car in a competition tomorrow.
(d) You are late for school tomorrow.
Solution
(a) Very unlikely for most places in Britain, especially in summer.
(b) Likely or Very likely in Britain in winter.
(c) Very unlikely if you have entered the competition. Impossible if you have not
entered the competition.
(d) Very unlikely, unless the school bus breaks down.
