SOLUTION: How many numbers from 1 to 20 inclusive must be on a blackboard before the probability of two of them being the same is greater than 1/2?

Question 260660: How many numbers from 1 to 20 inclusive must be on a blackboard before the probability of two of them being the same is greater than 1/2?

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
How many numbers from 1 to 20 inclusive must be on a blackboard before the probability of two of them being the same is greater than 1/2?
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Assume there are "x" numbers on the board.
You are picking with replacement.
P(you pick one of the "x" numbers on the next draw is x/20)
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Equation:
Solve x/20 > 1/2
x > 10
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Ans: x = 11
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Cheers,
Stan H.
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