Download Addition and Multiplication Counting Principle

Addition and Multiplication
Counting Principle
Addition Counting Principle
• There are m outcomes for Event 1
• There are n outcomes for Event 2
• If the problem asks for the probability of m
OR n, then you will add the probabilities
• Ex: coin & die
P(H OR 4)
P(H) + P(4)
½ + 1/6 Find the common denominator.
3/6 + 1/6
4/6 = 2/3
Example
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1 die
P(4 OR 5)
P(4) + P(5)
1/6 + 1/6
2/6 = 1/3
Multiplication Counting Principle
• There are m outcomes for Event 1
• There are n outcomes for Event 2
• If the problem asks for the probability of m
AND THEN n, then you will multiply the
probabilities
• Ex: coin & die
P(H AND 4)
P(H) x P(4)
½ x 1/6
1/12
Example
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1 die
P(4 AND 5)
P(4) x P(5)
1/6 x 1/6
1/36