Environmental Engineering Reference
In-Depth Information
4. Divide the sum by the number of test results (
n
).
5. Enter this number into the calculator.
6. Press “2nd” or “INV” then “LOG.”
7. See the geometric mean displayed on the calculator.
■
Example 6.4
Problem:
Given the data below, determine the geometric mean.
Week 1
12 MPN per 100 mL
Week 2
28 MPN per 100 mL
Week 3
37 MPN per 100 mL
Week 4
25 MPN per 100 mL
Solution:
1.079182
+
1.447158
+
1.568202
+
1.397940
4
Geometric Mean
=
Antilog
5.492481
4
=
Antilog
=
Antilog(1.373120)
=
23.6 MPN/100 mL
DID YoU KNoW?
Only a very few of the thousands of species of bacteria that exist
can cause an infectious disease in humans. Most cause no harm,
and in fact some provide essential services for the human body,
such as making vitamins or processing cellulose.
Viruses
Viruses
are parasitic particles—the smallest living infectious agents known.
Because they are parasitic entities, they are not cellular (have no nucleus, cell
membrane, or cell wall), are unable to multiply or adapt to the hostile water
environment, and lack a living host. They multiply only within living cells
(hosts) and are totally inert outside of living cells, but they still can survive
in the environment. Viruses differ from living cells in at least three ways: (1)
they are unable to reproduce independently of cells and cannot carry out cell
division; (2) they possess only one type of nucleic acid, either DNA or RNA;
and (3) they have a simple acellular organization (Prescott et al., 1993).
