Math 3118, Section 1
Fall 2002
Wednesday, December 4 class handout
Class exercises
-
Exercises from the text:
- Supplementary exercise #1
- One thousand students from School District M and one thousand students
from School District S took a test. For the students from District M, the
mean score was 75, and for the students from District S the mean score was 72.
- Assume that the standard deviation was 4 points for the District M students
and 6 points for the District S students. Determine how many
District M students and how many District S students had scores:
- 80 or above
- 85 or above
- 90 or above
- 70 or below
- 65 or below
- 60 or below
Suggestions: As in the exercises in the text, you need to
subtract the mean from the score in question (after shifting appropriately
by 1/2) and then divide by the standard deviation in order to get the
z-value.
For instance: If we're considering District M students,
then for scores of 80 or above we subtract the mean (=75) from 79.5 to get
a difference of 4.5 points. To find the z-value, we divide this difference
by the standard deviation (=4), obtaining 1.125 standard deviation units.
Thus, z is about 1.1.
Now, A(z) gives the area under the normal curve between
0 and z. We need the area under the curve which is
to the right of z, so we take note
of the fact that the total area under the right
half of the normal curve is .5 and proceed accordingly. (¿¿Should
we add or subtract??) The figure and discussion in
Information about the normal curve,
Part IA is relevent to this situation.
- Further exercises from the text
- Exercise 11.5.2
- Exercise 11.5.3
- Exercise 11.5.4
Homework due Monday, December 9
- Supplementary exercise #2
- One year later, one thousand students from School District M and
one thousand students from School District S took another standardized test.
This time, the mean score for the students from District M was 72, with
a standard deviation of 4.
For the students from District S the mean score was 75, with a standard
deviation of 6.
- Determine how many District M students and how many District S students
had scores:
- 80 or above
- 85 or above
- 90 or above
- 70 or below
- 65 or below
- 60 or below
Similar suggestions apply, as in supplementary exercise 1
above.
- Supplementary exercise #3
- Comment on the statement that "students from our district scored higher
than students from the other district". (A similar question is asked in
exercise 11.3.2 in the text.) Use information from the supplementary class
and homework exercises to illustrate your answers.
- In particular, discuss how the answers on the homework exercise were
different from the answers on the class exercise -- including not only
the obvious fact that the means have become switched. (For instance, the
differences toward one or the other end of the scale might not quite be
what the difference in means would lead us to expect.) Also, discuss any
aspects in which the comparisons may not have changed so dramatically.
- §11.5 #5
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