posted by tammy .
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.
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.