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A popular online retailer sells a wide variety of products including books. The proportion of customers that order only books is 21%. If a random sample of 600 customers is taken, what is the probability that more than 24% order only books?

  • statistics - ,

    Use the normal approximation to the binomial distribution.

    First find mean and standard deviation.

    mean = np = (600)(.21) = ?
    standard deviation = √npq = √(600)(.21)(.79) = ?
    Note: q = 1 - p

    I'll let you finish the calculations.

    Next take .24 times 600. Use that value for x in the z-score equation:
    z = (x - mean)/sd

    Once you calculate the z-score, look at a z-table to determine the probability. Remember that the problem is asking "more than" when you check the table.

    I hope this will help get you started.

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