Confidence interval calculator
Enter your values. The answer and the full worked solution update as you type.
Result
Lower limit49
Upper limit55.6
Margin of error3.302
Critical value2.064
Step-by-step solution
Critical value
t(24) = 2.064
Margin of error
E = t·s/√n = 2.064·8/√25 = 3.302
Interval
52.3 ± 3.302 → [49, 55.6]
Key formulas
- σ known
- x̄ ± z·σ/√n
- σ unknown
- x̄ ± t·s/√n, df = n − 1
- Critical z
- 90%: 1.645, 95%: 1.96, 99%: 2.576
- Sample size
- n = (z·σ/E)², rounded up
Practise Confidence intervals
A calculator gives the answer. In the exam you need the method: practise it with new problems, hints and worked solutions.
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