Question

Allen's hummingbird (Selasphorus sasin) has been studied by zoologist Bill Alther.† Suppose a small group of 12 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 σ = 0.20 gram.

(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

(b) What conditions are necessary for your calculations? (Select all that apply.)

n is large

normal distribution of weights

uniform distribution of weights

σ is unknown

σ is known

(c) Interpret your results in the context of this problem. (select all that apply)

The probability to the true average weight of Allen's hummingbirds is equal to the sample mean.

The probability that this interval contains the true average weight of Allen's hummingbirds is 0.20.    

There is a 20% chance that the interval is one of the intervals containing the true average weight of Allen's hummingbirds in this region.

There is an 80% chance that the interval is one of the intervals containing the true average weight of Allen's hummingbirds in this region.

The probability that this interval contains the true average weight of Allen's hummingbirds is 0.80.

(d) Find the sample size necessary for an 80% confidence level with a maximal margin of error E = 0.06 for the mean weights of the hummingbirds. (Round up to the nearest whole number.)
__________ hummingbirds

Answer 1

Given : Sample size=n=12

Sample mean=

Population standard deviation=

Significance level=

(a) The 80% confidence interval for the average weights of Allen's hummingbirds in the study region is ,

; From the standard normal probability table ,

The margin of error is ,

Lower limit=3.08

Upper limit = 3.22

(b) The necessary conditions for your calculations are

n is large

normal distribution of weights

σ is known

(c) Interpretation :

There is an 80% chance that the interval is one of the intervals containing the true average weight of Allen's hummingbirds in this region.

(d) Since , the margin of error=E=0.06

Therefore , the required sample size is ,