Wastewater samples taken from an industrial discharge had the chemical oxygen demand (COD) concentrations below in mg/L. Determine the (a) arithmetic mean (by hand and spreadsheet), (b) median, (c) mode, and (d) standard deviation (by hand and spreadsheet).
COD values: 452, 364, 415, 395, 404, 470, 391, 395, 425, 430, 380
(a) Mean = (452 + 364 + 415 +………+ 380)/11
= 411 mg/L
(b) Arrange values in increasing order and select middle value (i.e. 6th one)
Arranged values: 364,380,391,395,395,404,415,425,430,452,470
Median = 404 mg/L
(c) For mode, select value which occurs most frequently
Mode = 395 mg/L
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