Question

The Environmental Protection Agency (EPA) is concerned about the amount of chloride in household water supplies. In a sample of 18 households, the amounts (in mg/L) of chloride was recorded, as follows:

16 0 0 2 3 6 8 2 5 0 12 10 5 7 2 8 6 9

(a) Calculate the mean, standard deviation and standard error of the mean for the above data.

(b) Construct and interpret a 98% confidence interval for the true mean amount of chloride in the water supply of all households.

(c) Without doing further calculations, would a 95% confidence interval be wider, narrower or the same width as the confidence interval in (b)? Explain your answer.

(d) The EPA is concerned that using a sample of 18 households does not contain enough information to adequately estimate the true mean chloride levels. It decides to take a larger sample of 2400 households and computes a mean chloride level of 3.78 mg/L and a variance of 15.45 (mg/L)2 . Using these data, construct and interpret a 95% confidence interval for the true mean chloride levels of all households.

(e) Corrective action must be taken if chloride levels exceed 5mg/L. Based on the confidence interval in (d), should corrective action be taken? Briefly justify your answer.

Answer 1

dotb secerdd 6,0,0,2,36 212 12, 05 7,286 en gives anunt of chuo ide (ma/L) then ) Samp 5.6 に, -1) 4.43 々 : 1.0千 b) ASseurni c2. is net known 13 yn

ⓒAnce the-arta-in-乜tewiss.ouestionsfigwe.B 0s 2 9 6 92% centidorce intervul fe-rus mean is : (3.62, 3.4 which 5 nA/L mean lies beturen 3.62 & 3.94