If the odd favoring an event are 10 to 1, then the probability
of the event occurring is 0.9.
The odds in favor of an event are 10:1.
Find the probability that the event will occur.
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P(E)+P(E') = 1
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P(E)/P(E') = 10/1
So P(E) = 10P(E')
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Substitute for P(E) and solve for P(E'):
10P(E')+P(E') = 1
11P(E') = 1
P(E') = 1/11
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Therefore P(E) = 10/11