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. All observations were below the allowable maximum, as shown by the reported range of contaminant levels. (presumably the mean would be the midrange).
 

  Substance Range Detected Allowable
Maximum Origin of Substance   Chromium 0.41 to 0.60 100 Discharge from steel and pulp mills, natural erosion   Barium 0.006 to 0.020 2 Discharge from drilling wastes, metal refineries, natural erosion   Fluoride 1.09 to 1.15 4 Natural erosion, water additive, discharge from fertilizer and aluminum factories        

For each substance, estimate the standard deviation σ 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    

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Item 8                            Item 8                                                                2          points                                      Item          Skipped     High levels of cockpit noise in an aircraft can damage the hearing of pilots who are exposed to this hazard for many hours. Cockpit noise in a jet aircraft is mostly due to airflow at hundreds of miles per hour. This 3 × 3 contingency table shows 61 observations of data collected by an airline pilot using a handheld sound meter in a certain aircraft cockpit. Noise level is defined as “low” (under 88 decibels), “medium” (88 to 91 decibels), or “high” (92 decibels or more). There are three flight phases (climb, cruise, descent).
Cockpit Noise Flight Phase Noise LevelClimb (B)Cruise (C)Descent (D)Row TotalLow (L) 5  8  5  18 Medium (M) 16  7  2  25 High (H) 6  5  7  18 Column Total 27  20  14  61  
 Click here for the Excel Data File

(a) Calculate the following probabilities: (Round your answers to 4 decimal places.)
    i.P(B)  ii.P(L)  iii.P(H | C)  iv.P(H | D)  v.P(L and B)  vi.P(L and C)   (b) Do you see evidence that noise level depends on flight phase?
 

Yes
No