Mathematics · University
Variance of a binomial count · formula reference
Assume a fixed number of independent trials with the same success probability.
Formula
Assume a fixed number of independent trials with the same success probability.
Var(X) = np(1−p)
Worked example
Let X be binomial with n = 160 and success probability p = 0.4. Find Var(X). Round the final result to 4 decimal places if needed.
Independent Bernoulli variances add: 160 × 0.4 × (1 − 0.4).
38.4
Prerequisites and checking
Algebra; calculus or linear algebra as appropriate to the topic. Keep units and rounding consistent. State the model conditions before applying the formula.
Further reading and review references
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