Biological oxygen demand (BOD) is an index of pollution that is monitored in the

Question

Biological oxygen demand (BOD) is an index of pollution that is monitored in the treated effluent of paper mills on a regular basis. From 120 determinations of BOD (in pounds per day) at a particular paper mill during the sprinng and summer months of 199, the sample mean and the sample standard deviation were found to be 5720 and 1710 pounds per day, respectively. Do these results constitute statistical evidence for the state's claim that the true mean BOD is greater than 5500 pounds per day? Answer using the p-value.

Explanation / Answer

Hypothesis;
H0 : mu = 5500
Ha : mu > 5500

Test statistics:

x = 5720 , s = 1710 , n = 120

z = ( x -mean)/(s/sqrt(n))
= (5720 - 5500)/(1710/sqrt(120))
= 1.4093

p value = 0.0794 at 0.05 significance level

we cannot reject the null hypothesis at 0.05 significance level

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