A social worker at a large high school wants to estimate the number of days students are absent. He randomly

selects 45 students and records the number of days each one is absent. The social worker constructs a 95%

confidence interval for the true mean number of days students at this school are absent. Which of the following

would decrease the margin of error?

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using a sample of size 30

using a sample of size 40

constructing a 90% confidence interval

constructing a 99% confidence interval