Statistics

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For a normal distribution with a mean of m = 80 and a standard deviation of s = 20, find the proportion of the population corresponding to each of the following scores.

a. Scores greater than 85
b. Scores less than 100
c. Scores between 70 and 90

I believe this is the correct formula to start with but am unclear on how to finish it. Any help would be appreciated.

a. z = X-m= 85–80 = 5 = 0.25
s 20 20

b. z = X-m= 100–80 = 20 = 1.00
s 20 20

c. z = X-m= 70–80 = -10 = -0.25
s 20 20
z = X-m= 90–80 = 10 = 0.50
s 20 20

  • Statistics -

    What does "s 20 20" mean?

    Z = (x-mean)/SD

    Type equation completely to avoid mistakes.

    c. -10/20 = ?

    Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores you have found.

    I hope this helps.

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