- Fraction Calculator
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- Algebra Calculator
- Trigonometry Calculator
- Percentage Calculator
- Probability Calculator
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Monty Hall Problem Probability CalculatorCalculate the Monty Hall problem odds for any number of doors. See why switching wins (d−1)/d of the time and staying only 1/d.
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Confidence Interval for a Proportion CalculatorCompute a confidence interval for a population proportion from successes and sample size at 90%, 95%, or 99% confidence using the normal (Wald) approximation.
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One-Sample t-Test CalculatorCompute the one-sample t-test statistic from the sample mean, population mean, standard deviation, and size. Get t, degrees of freedom, and standard error.
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Standard Error of the Mean (SEM) CalculatorCalculate the standard error of the mean (SEM) instantly from the sample standard deviation and sample size using SEM = s / √n.
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One-Sample t-Test CalculatorCalculate the one-sample t-test statistic from sample mean, hypothesized mean, standard deviation and sample size. Get t, standard error and degrees of freedom.
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Chi-Square Test Statistic CalculatorCalculate the chi-square (χ²) test statistic from observed and expected frequencies. Free goodness-of-fit calculator with degrees of freedom.
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Weighted Mean CalculatorCalculate the weighted mean (weighted average) from a set of values and their weights. Enter comma-separated values and weights to get the result instantly.
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Percentile to Z-Score CalculatorConvert any percentile (0–100) into a standard normal z-score using the inverse normal CDF, z = Φ⁻¹(p). Fast, accurate, and free.
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P-Value from Z-Score CalculatorConvert a Z-score to a P-value for one-tailed or two-tailed hypothesis tests. Uses the standard normal distribution to compute statistical significance.
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Sample Size Calculator (Proportion)Calculate the required survey sample size for estimating a proportion at a given confidence level and margin of error using n = z²·p(1−p)/E².
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Chi-Square Test of Independence Calculator (2x2)Run a 2x2 chi-square test of independence online. Enter your contingency table cells to get χ², degrees of freedom, p-value, and significance at α = 0.05.
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P-Value from t-Score CalculatorConvert a Student's t-score and degrees of freedom into a p-value. Supports one-tailed and two-tailed tests with exact incomplete-beta computation.
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Complement Probability CalculatorCalculate the complement probability P(A') = 1 − P(A) instantly. Enter the probability of an event and find the chance it does NOT happen.
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Five-Number Summary CalculatorFind the five-number summary (minimum, Q1, median, Q3, maximum) plus IQR for any data set. Free online statistics calculator with worked examples.
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Cohen's d Effect Size CalculatorCalculate Cohen's d effect size from two group means, standard deviations and sample sizes, with pooled SD and a small/medium/large interpretation.
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Critical t Value CalculatorFind the critical t value for any significance level (α) and degrees of freedom. Supports one-tailed and two-tailed tests using the t distribution.
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Spearman's Rank Correlation CalculatorCalculate Spearman's rank correlation coefficient (ρ) from paired X and Y data. Handles ties, shows Σd² and n. Free statistics tool.
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Critical Z Value CalculatorFind the critical z value (z*) from any confidence level using the inverse normal CDF. Supports two-tailed and one-tailed tests. Free and instant.
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Combination Calculator (nCr)Calculate combinations without repetition (nCr) instantly. Enter n and r to find how many ways you can choose r items from n where order does not matter.
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Sample Mean (Average) CalculatorCalculate the sample mean (average) of any data set. Enter your numbers and get x̄ = Σxi / n with sum and count instantly.
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Permutation (nPr) CalculatorCalculate permutations nPr = n! / (n−r)! instantly. Find the number of ordered arrangements when choosing r items from n. Free, fast, and accurate.
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Return Period & Exceedance Probability CalculatorCalculate the probability that a storm or flood with return period T is exceeded at least once over n years. Free hydrology risk calculator.
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Discrete Probability Distribution CalculatorCompute the mean, variance and standard deviation of a discrete probability distribution from a table of values and probabilities. Free and instant.
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Interquartile Range (IQR) Outlier CalculatorFind Q1, Q3, IQR and detect outliers with the 1.5×IQR Tukey rule. Computes lower and upper fences from your data set instantly.
