Allen's hummingbird (Selasphorus sasin) has been studied by zoologist Bill Alther.† Suppose a small group of 16 Allen's hummingbirds has been under study in Arizona. The average weight for these birds is x = 3.15 grams. Based on previous studies, we can assume that the weights of Allen's hummingbirds have a normal distribution, with ? = 0.38 gram. When finding an 80% confidence interval, what is the critical value for confidence level? (Give your answer to two decimal places.) zc =   (a) Find an 80% confidence interval for the average weights of Allen's hummingbirds in the study region. What is the margin of error? (Round your answers to two decimal places.) lower limit upper limit margin of error        Find the sample size necessary for an 80% confidence level with a maximal margin of error E = 0.12 for the mean weights of the hummingbirds. (Round up to the nearest whole number.)   hummingbirds

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Allen's hummingbird (Selasphorus sasin) has been studied by zoologist Bill Alther.† Suppose a small group of 16 Allen's hummingbirds has been under study in Arizona. The average weight for these birds is x = 3.15 grams. Based on previous studies, we can assume that the weights of Allen's hummingbirds have a normal distribution, with ? = 0.38 gram.
When finding an 80% confidence interval, what is the critical value for confidence level? (Give your answer to two decimal places.)
zc =  
(a)
Find an 80% confidence interval for the average weights of Allen's hummingbirds in the study region. What is the margin of error? (Round your answers to two decimal places.)
lower limit upper limit margin of error 
 
 
 
Find the sample size necessary for an 80% confidence level with a maximal margin of error E = 0.12 for the mean weights of the hummingbirds. (Round up to the nearest whole number.)
  hummingbirds
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Follow-up Question

obs and productivity! How do retail stores rate? One way to answer this question is to examine annual profits per employee. The following data give annual profits per employee (in units of 1 thousand dollars per employee) for companies in retail sales. Assume ? ≈ 3.8 thousand dollars.

4.1
6.7
3.6
8.2
8.2
6.0
8.9
6.3
2.6
2.9
8.1
−1.9
11.9
8.2
6.4
4.7
5.5
4.8
3.0
4.3
−6.0
1.5
2.9
4.8
−1.7
9.4
5.5
5.8
4.7
6.2
15.0
4.1
3.7
5.1
4.2
(a) Use a calculator or appropriate computer software to find x for the preceding data. (Round your answer to two decimal places.)
 thousand dollars per employee

(b) Let us say that the preceding data are representative of the entire sector of retail sales companies. Find an 80% confidence interval for ?, the average annual profit per employee for retail sales. (Round your answers to two decimal places.)
lower limit      thousand dollars
upper limit      thousand dollars
   
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