Question

The Environmental Protection Agency (EPA) requires that cities monitor over 80 contaminants in their drinking water. Samples from the Lake Huron Water Treatment Plant gave the results shown here. Only the range is reported, not the mean. Substance MCLG Range Detected Allowable MCLG Origin of Substance Chromium 0.47 to 0.69 100 Discharge from steel and pulp mills, natural erosion Barium 0.004 to 0.019 2 Discharge from drilling wastes, metal refineries, natural erosion Natural erosion, water additive, Fluoride 1.07 to 1.17 4.0 discharge from fertilizer and aluminum factories MCLG = Maximum contaminant level goal For each substance, estimate the standard deviation o by assuming uniform distribution and normal distribution shown in Table 8.11 in Section 8.8. (Round your answers to 4 decimal places.) uniform distribution normal distribution Chromium Barium Fluoride

Answer 1

from uniform distribution : standard deviation =range/sqrt(12)

for normal distribution : standard deviation =range/6

a	b		uniform distribution	Normal distribution
0.47	0.69	Chromium	0.0635	0.0367
0.004	0.019	Barium	0.0043	0.0025
1.07	1.17	Fluoride	0.0289	0.0167