Probability based on Z score
1. For a sample selected from a population with a mean of
µ=50 and a standard deviation of σ = 10:
a. What is the expected value of M and the standard error of
M for a sample of n=4 scores?
b. What is the expected value of M and the standard error of
M for a sample of n = 25 scores?
2. A population has a mean of µ = 80 and a standard
deviation of σ = 10. If you selected a random sample of n = 25 scores,
how much error would you expect between the sample mean and the population
mean?
3. A population forms a normal distribution with a mean of µ
= 75 and a standard deviation of σ = 20.
Sketch the distribution of sample means for samples of n =
100. What proportion of the sample means for n = 100 have values greater than
79? In other words, find p(M>79) for n = 100.
4. A normal-shaped distribution has µ=80 and σ =
15. Sketch the distribution of sample means for samples of n = 25 scores from
this population. Compute the z-scores for M = 89 for a sample of n = 25 scores.
Is this sample mean in the middle 95% of the distribution?





