Question 310465
What is the probability of rolling a red and a green number cube and getting:
A sum of 7 OR 11?
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Ways to get 7: 1/6;2/5;3/4;4/3;5/2;6/1----------6 ways
Ways to get 11: 5/6;6/5-------------------------2 ways
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P(sum of 7 or 11) = P(7)+P(11) = (6+2)/36 = 2/9
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A prime number on red OR a two on green?
Ways to get red prime: 2/1;2/2;2/3;2/4;2/5;2/6
-----------------------3/1;3/2;3/3;3/4;3/5;3/6
-----------------------5/1;5/2;5/3;5/4;5/5;5/6
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Ways to get 2 on green: 1/2;2/2;3/2;4/2/5/2;6/2

P(red prime OR green two) = P(red prime) + P(green 2) - P(red prime and green 2)
= (18/36) + (6/36) - (3/36) = 21/36
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Cheers,
Stan H.
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