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16 Probability

On Sunday 3 June 2012 there was a Jubilee Pageant in London. Key words

1000 boats travelled down the River !ames through the city
of London. Make sure you learn and

!e pageant was held to celebrate the fact that Queen Elizabeth II understand these key words:
had been on the throne for 60 years. mutually exclusive
!e pageant started at 14:30 and lasted about 3 hours. sample space diagram

relative frequency
!e chart below shows a weather forecast for London on that day.

City of Londen Youth Hostel
Air
Sun 3 Jun
Wind speed Precipitation Quality
UK local Regional Temperature & direction Wind gusts Probability Feels like UV index
time warnings Weather (˚C) (mph) (mph) Visibility Humidity (%) (%) (˚C) index [BETA]
0100 No warnings 10 11 24 Moderate 91 80 8 0

0400 No warnings 10 12 26 Moderate 95 80 8 0

0700 No warnings 10 11 24 Moderate 95 80 7 1

1000 No warnings 10 10 No gusts Moderate 93 80 8 1
2
1300 No warnings 10 8 No gusts Moderate 94 80 8 1

1600 No warnings 10 7 No gusts Moderate 92 80 8 1

1900 No warnings 10 6 No gusts Moderate 91 60 8 1

2200 No warnings 9 5 No gusts Moderate 93 60 8 0
Issued at 0900 on Fri 1 Jun 2012

!e forecast was made on Friday morning, two days before the pageant. It predicted the weather every
two hours through the day.
One column show the probability of precipitation – that means rain or snow.
!e probability is given as a percentage.

!e forecast reported an 80% chance of heavy rain during the pageant. It advised that the thousands of

spectators should take umbrellas. !ere should be no gusts of wind during the pageant.

Weather forecasts are produced by complex computer programs. !ey are available for thousands of

places throughout the world. !ey are updated regularly. You can easily "nd them on the internet. Try

to "nd one for a place near where you live.

On the day of the pageant it was dry until about 16:00. A#er that it rained steadily. !ere were no gusts

of wind.
In this unit, you will learn more about predicting probabilities.

16 Probability 151