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Question

In a survey, 13 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $34 and standard deviation of $4. Find the margin of error at a 99% confidence level.

Give your answer to two decimal places

Answer 1

Since population standard deviation is unknown and sample size is 13 we would use the t-critical value for alpha/2 = 0.005 and 12 degrees of freedom in the computation of the standard error:

standard error = t-critical (0.005, 12) * standard deviation/square root(13)