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Exercise: <<
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Maths
Exercise 8 - Probability
Probability covers the likelihood of an event occurring and expresses that likelihood
as a mathematical figure (normally a percentage or a
fraction).
For example the likelihood of having homework tonight is probably very high, where as the
likelihood of jumping over your home is very small.
To understand the likelihood's please place the following statements in order of their
likelihood (put the most likely to happen first).
1. The Sun will set tonight and rise tomorrow.
2. I will grow two more arms over the next day.
3. I am left handed.
4. I will have homework.
Answers: 1, 4, 3, 2
The Probability Scale
The probability scale starts at 0 and finishes at 1. Something that is impossible to occur is rated 0 and something that is certain to happen is rated at 1.
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0 |
1/2 |
1 |
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Impossible |
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Certain |
The likelihood that all the oceans will freeze over is 0. The likelihood that it will be dark tonight is 1.
Existing Probability
1. Consider tossing a coin. It can either land on heads or tails so there are 2 outcomes. The probability of a coin landing on heads is 1 out of 2 or 1/2.
2. Consider rolling a die. It has an equal chance of landing on 1, 2, 3, 4, 5 or 6. Hence there are six outcomes. The probability of a die landing on 4 is 1 out of 6 or 1/6.
3. Consider the days of the week. All the days of the week are written on
separate bits of paper and put in a bag.
What is the likelihood of picking a weekend day ( Saturday or Sunday) from the bag. There are seven possible outcomes and two potential correct outcomes. The probability of picking a Saturday or Sunday is 2 out of 7 or 2/7.
In all of the three examples above the probability is calculated as
Probability = no. of chances divided by total no. of outcomes
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