Weight of a rock: In a geology course, students are learning to use a balance sc
ID: 3249375 • Letter: W
Question
Weight of a rock: In a geology course, students are learning to use a balance scale to accurately weigh rocks. One student plans to weigh a rock 20 times and then calculate the average of the 20 measurements to estimate her rock's true weight. A second student plans to weigh a rock 5 times and calculate the average of the 5 measurements to estimate his rock's true weight. Suppose the students construct a 95% confidence interval for the true weight of their rocks. Whose interval do you expect to be more precise (narrower)?
A)The student who weighed the rock 20 times.
B)The student who weighed the rock 5 times
.C) Both intervals would be equally precise.
According to a home securities company, the highest percentage of home burglaries occur during the summer months. Local police conducted a study of home burglaries for a ten-year period. A computer program randomly selected 1500 home burglaries and both the month of burglary and amount of insurance claim were recorded. Of the 1500 home burglaries analyzed in the study, 39% of burglaries occurred in summer months (June, July, August). The average insurance claim was $2,100.
Determine if the following critique of the study is valid or invalid.
A citizen group believes the study results are not statistically significant because the local police analyzed only 1500 home burglaries when there were over 9000 home burglaries in the ten-year period. Is the citizen group critique valid or invalid?
Valid
Invalid
Explanation / Answer
In calculating the margin of error, the sample size come into denominator. So as the sample size increases margin of error decreases. That is confidence interval become narrower.
So following option is correct:
A)The student who weighed the rock 20 times.
----------------------
It is invalid. Because sample size is fairly large in comparison to population size.
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