How do you find probabilities of compound events?

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How do you find probabilities of compound events?

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Answer 1 · 2017-11-18T12:03:11

Depends on the relation between the events.

Explanation:

Example1: probability of rolling a 3 or a 5 with one throw.
$P (3) = \frac{1}{6}$ $P(3)=1/6$ , $P (5) = \frac{1}{6}$ $P(5)=1/6$
Since this is an exclusive OR situation we ADD the probabilities:
$P (3 or 5) = P (3) + P (5) = \frac{1}{6} + \frac{1}{6} = \frac{1}{3}$ $P(3or5)=P(3)+P(5)=1/6+1/6=1/3$

Example2: probability of first rolling a 3, and then a 5 with one die.
1st roll: $P (3) = \frac{1}{6}$ $P(3)=1/6$ , 2nd roll: $P (5) = \frac{1}{6}$ $P(5)=1/6$
Since this is an AND situation, we MULTIPLY:
$P (3, 5) = \frac{1}{6} \times \frac{1}{6} = \frac{1}{36}$ $P(3,5)=1/6xx1/6=1/36$
Note: if the question were about 'a 3 and a 5' (in any order) we'd have to add: $P (5, 3) = \frac{1}{36}$ $P(5,3)=1/36$

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How do you find probabilities of compound events?

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