CONTENTS - Department of Mathematics and Statistics - University ...

2. Exam 2005
An ecologist must determine whether a cleanup
project at a lake has been effective. This is to be
done by recording dissolved oxygen content (in
parts per million, ppm) in the lake, with higher
values indicating less pollution. Prior to the
cleanup project a random sample of 50 dissolved
oxygen readings was recorded around the lake. Six
months after the initiation of the cleanup a second
random sample of 70 readings was recorded.
Results are summarised in the following table.
Before Cleanup After Cleanup
Sample Size (n i ) 50 70
Sample Mean ( x i ) 10.30 10.46
2
s 0.32 0.36
Sample Variance ( )
i
(a) (1 mark) State null and alternative hypotheses
for testing the data driven hypothesis that the
cleanup has resulted in an increase in the
dissolved oxygen content.
Null hypothesis, H 0 : μ BC = μ AC
Alternative hypothesis, H A : μ BC < μ AC
251
Section 6