Petroleum pollution in oceans is known to increase the growth of a certain bacteria. Brian did a project for his ecology class in which he made a bacteria count (per 100 milliliters) in nine random samples of sea water. His counts gave the following readings:

17, 23, 18, 19, 21, 16, 12, 15, 18

a) Find the range.

b) Find the sample mean.

c) Find the median.

d) Find the mode.

e) Find the sample standard deviation.


a) The range is 21 – 12 = 9.

b) The sample mean is

c) The median is 17.5 as well.

d) The mode is 18.

e) The sample standard deviation is