An environmentalist would like to estimate the true mean weight of all cars. To do so, she selects a random sample of 30 cars and determines that the 90% confidence interval for the true mean weight to be 2.8 to 3.4 tons. Which of the following would increase the margin of error for this confidence interval?

The margin of error is the distance from the sample mean to either endpoint of the interval, and it depends on the confidence level and sample size. Increasing the confidence level requires a wider interval to be more likely to contain the true mean, so the margin of error increases. Increasing the sample size would instead make the margin of error smaller.

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