1
Practice
Midterm Exam for Stat 102
Instructions
: The exam itself will be a semi-closed book exam. One page of notes (or
one page - two-sided) will be allowed. When performing hypothesis tests, clearly state
the null and alternative hypotheses and show the critical value and/or P-value (from the
table) where appropriate. Normal tables, t-tables and F-tables copied from your text are
provided.
Write your answers on the test and always show your work.
Partial credit will
be given.
Time:
90 minutes
.
1.
When gasoline is pumped into the tank of an automobile, hydrocarbon vapors in
the tank are forced out and into the atmosphere. This is undesirable, and vapor-recovery
devices are usually installed on gasoline pumps in order to reduce the emission of these
vapors. It is difficult and expensive to test a recovery device in actual operation, and so
tests of new devices typically involve only a modest number of trials of the device.
Data was gathered measuring the hydrocarbon emissions while filling a gas tank
for two types of vapor-
recovery device: a “regular” device and a new, “improved” design.
The following analysis is for a sample of 50 observations of hydrocarbon emissions (in g)
using the new and hopefully improved type of device, and 75 observations using the
standard device.
Here is a table from JMP showing the means and standard deviations of the two
samples:
Means and Std Deviations
Level
Number
Mean
Std Dev
Std Err Mean
Lower 95%
Upper 95%
Improved
50
28.46
6.178
0.8737
26.70
30.22
Regular
75
31.99
9.232
1.0660
29.86
34.11
Does the “improved” design appear to change the level of hydrocarbon vapors
emitted? Set up appropriate hypotheses and carry out the test at 0.05 level. [You may use
whichever method seems appropriate to you
–
the equal population variance method or
the unequal population variance method. If you use the latter method, you may assume its
DF number is DF
100.]

This
** preview**
has intentionally

**sections.**

*blurred***to view the full version.**

*Sign up*