Inference Practice
Build and interpret confidence intervals, set up hypotheses, compute test statistics and p-values, and conclude without overclaiming.
1 Practice
Type your answer and press Check answer (or Enter). A wrong answer earns a hint; a second miss earns a stronger hint; a third miss walks you through the full solution. Scores and streaks are session-only.
2 What you’ll practice
Every problem is generated fresh from templates across several question types — a problem never repeats until its whole pool is used up.
Margin of error
z* × σ/√n.
Proportion CI
p̂ ± z*√(p̂(1−p̂)/n).
CI interpretation
Confidence describes the method.
Hypotheses
H0 has =; Ha has the suspicion.
z-statistic
(x̄−μ₀)/SE.
p-value conclusion
p < α → reject; never "prove".
3 Watch out for these
The mistakes students make most often on these problems.
Say “we are 95% confident the true mean is between a and b” — 95% is the method’s long-run rate.
Small p rejects H0; it does not prove Ha or measure importance. Conclude in context.
“Fail to reject” is not “accept” — the evidence was just not convincing.