Statistics (STAT 101) Confidence Intervals, Margin of Error, and Sample Size Practice Problems
University of Florida
Statistics (STAT 101) | Practice Problems

Overview
A practice packet focused on building and interpreting confidence intervals for means and proportions, connecting margin of error to n, and planning sample sizes for finals.

Key topics
•CI for mean (t) vs CI for proportion (z)
•margin of error formulas and what controls it
•critical values and confidence level
•sample size planning for mean/proportion
•interpreting CIs in plain language

Suggested study tasks
•compute 6 confidence intervals (3 means, 3 proportions) with correct critical values
•solve 5 margin-of-error questions by isolating n
•choose z* values for 90%, 95%, and 99% confidence
•interpret 4 intervals in context (parameter, units, scope)
•check assumptions for each problem before computing the interval

Common pitfalls
•using z when t is required for a mean with unknown ?
•plugging p-hat into n planning without using a conservative estimate when needed
•confusing confidence level with probability the parameter is in the interval
•mixing up standard deviation with standard error
•rounding n down in sample size calculations