Psy 555 Homework 4

Chapter 3 # 1, 2, 3, 4, 6

1. Answer the following questions using the frequency distribution below (also fill in the blanks on the table).

a) Draw a frequency distribution with this data set.

b) What is the 45th percentile?

c) What is the 75th percentile

d) What is the percent rank for X=5?

e) What is the minimum score needed to be in the top 25% of the distribution?

f) Is this distribution normal?

 X Freq Cum Freq Cum % 6 22 100% 5 4 4 16 3 4 45% 2 4 1 2 2 9%

2.A population has a m=80 and s=20.  Find the z-score that corresponds to each of the following X values (rounding to 2 decimal places, e.g., z=2.25):

85, 100, 120, 75, 65, 60, 130, 82, 68, 80, 105, 30

3. A population is made up of the following scores:

13, 17, 21, 15, 16, 31, 23, 14, 27, 28

a) Compute m and s.

b) Find the z-score for each of the raw scores of the population (rounding to 2 decimal places, e.g., z=2.25).

4. For a population with m=85, a raw score of 72 corresponds to a z-score of -1.00.  What is the standard deviation of this population?