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Confidence Interval Calculator — Mean (z/t) & Proportion with Steps

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Interval for Confidence level Sample mean Standard deviation Use sample s for t mode or population σ for z mode.Sample size n Must be a whole number greater than 1.Displayed precision

Calculated result

95% CI: 65.808 to 78.192

Estimate: 72

Standard error: 3

t* (df 24): 2.064

Margin of error: 6.192

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1. SE = 15 ÷ √25 = 3.
2. Because population σ is unknown, use a two-sided t critical value with df = n−1.
3. Margin = 2.064 × 3 = 6.192.
4. Interval = 72 ± 6.192 = 65.808 to 78.192.

The t interval assumes the sample/design conditions for mean inference are reasonable. For df above 30, MAXScanner uses a standard asymptotic t-quantile expansion; differences from statistical packages should be tiny at the displayed precision.

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