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For a normal distribution with a mean of 140 and a standard deviation of 55 find each value requested.

a. What is the minimum score needed to be in the bottom 10% of the distribution?

b. What scores form the boundaries for the middle 75% of the distribution.

  • statistics -

    Z = (score-mean)/SD

    Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion (.10) related to the Z score. Insert values to find score.

    Middle 75% = ± .375 between score and mean. Use the same table.

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