Cambridge International Mathematics

The probability line below shows words which can be used to describe the chance of an event occurring.

EXERCISE 25A

1 Assign suitable words or phrases to these probability calculations:

a 0 b 0 : 51 c 10001 d 0 : 23 e 1 f^12 %

g 0 : 77 h 0 : 999 i^1526 j 1999500 k 0 : 002 l^1720

2 Suppose that P(A)=^13 ,P(B) = 60% and P(C)=0: 54.

Which event is: a most b least likely?

3 Use words to describe the probability that:

a the maximum temperature in London tomorrow will be negative

b you will sleep in the next 48 hours

c Manchester United will win its next football match

d you will be eaten by a dinosaur

e it will rain in Singapore some time this week.

Sometimes the only way of finding the probability of a particular event occurring is by experimentation or

using data that has been collected over time.

In a probability experiment:

² Thenumber of trialsis the total number of times the experiment is repeated.

² Theoutcomesare the different results possible for one trial of the experiment.

² Thefrequencyof a particular outcome is the number of times that this outcome is observed.

² Therelative frequencyof an outcome is the frequency of that outcome divided by the total number of

trials.

relative frequency=

frequency

number of trials

For example, when tossing a tin can in the air 250 times, it comes

to rest on an end 37 times. We say:

² the number of trials is 250

² the outcomes areendsandsides

² the frequency ofendsis 37 andsidesis 213

² the relative frequency ofends = 25037 ¼ 0 : 148

² the relative frequency ofsides =^213250 ¼ 0 : 852.

B ESTIMATING PROBABILITY [10.2, 10.6]

0 1

impossible very unlikely unlikely equally

likely

likely very likely certain

extremely

unlikely

extremely

likely

Qw_

Probability (Chapter 25) 507

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Y:\HAESE\IGCSE01\IG01_25\507IGCSE01_25.CDR Monday, 27 October 2008 2:30:38 PM PETER