SOLUTION: a school bus contains 8 first graders and 10 second graders. if two children are are what is the probability that at least one is a second grader.

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Question 232448: a school bus contains 8 first graders and 10 second graders. if two children are are what is the probability that at least one is a second grader.
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
a school bus contains 8 first graders and 10 second graders. if two children are are what is the probability that at least one is a second grader.
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P(selecting a second grader) = 10/18 = 5/9
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Your Problem:
P(at least one) + P(none) = 1
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P(at least one second grader among 2 selected)
= 1 - P(no second grader amoung two selected)
= 1 - 2C0(5/9)^0(4/9)^2 = 1- (4/9)^2 = 1-16/81 = 65/81
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Cheers,
Stan H.