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Statistics and Probability

Quick questions on Basic probability explained: N(A)-Level Mathematics Statistics and Probability

4short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is the probability scale?
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Probability measures how likely something is, on a scale from 00 to 11:
What are equally likely outcomes?
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When all outcomes are equally likely (a fair die, a well-shuffled pack), the probability of an event is:
What is counting outcomes carefully?
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The key step is counting correctly. List the favourable outcomes and the total outcomes, then form the fraction. For "an even number on a die", the favourable outcomes are 2,4,62, 4, 6 (three of them), so the probability is 36=12\dfrac{3}{6} = \dfrac{1}{2}.
What is the complement rule?
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The outcomes of an event and its opposite (its complement) together cover everything, so their probabilities add to 11:

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