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Suppose the final exam scores in a large class is symmetric mound shaped with a mean of 70 points and standard deviation of 10 points. The percentage of students in the class who receive more than 60 points is approximately

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  1. Use z-scores.

    Formula:
    z = (x - mean)/sd

    x = 60
    mean = 70
    sd = 10

    Substitute into the formula and find z. Use a z-distribution table to find the probability. Convert to a percent.

    I hope this will help get you started.

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  2. 60% is 70%-10% (1 standard deviation).

    Look up a normal distribution table (or
    http://www.mathsisfun.com/data/standard-normal-distribution-table.html
    )
    to find that at Z=1 (1 standard deviation) below mean is (0.5)-0.3413=0.1587
    So 15.87% of the class has (70-10)=60% or less. So how many are above 60?

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