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Math-Probability

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An urn contains four red balls and three white balls. A sample of 2 balls is selected at random from the urn. What is the probability that at least one of the balls is red?

  • Math-Probability - ,

    number of ways to pick any two = C(7,2) = 21
    number of ways with only white = C(3,2) = 3
    so the number of ways with at least one red = 21-3 = 18
    prob of at least 1 red = 18/21 = 6/7

  • Math-Probability - ,

    what does c stand for and how do you get 21?

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