Find the mean first = sum of scores/number of scores
Subtract each of the scores from the mean and square each difference. Find the sum of these squares. Divide that by the number of scores to get variance.
Standard deviation = square root of variance
Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (.80) and its Z score. Insert Z score into equation above.
The following are weights (in lbs) for a sample of 11 baby boys at the age of 18 months:
21.8
22.2
23.4
24.6
25.1
26.7
27.3
28.0
29.8
30.9
31.2
What is the 80th percentile estimate for these sample?
1 answer