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Boy-or-Girl Conditional Probability Calculator — result sheet
Calculate the probability that both children are girls after a selected at-least-one-girl observation model.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Given at least one girl under the family-level observation model, P(two girls)=p²/(1−(1−p)²).
The observation rule is named because conditional probability changes when the information is generated by a family statement rather than a randomly selected child.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Probability a child is a girl — minimum 0; maximum 1
Worked example
| Input | Value |
|---|---|
| Probability a child is a girl | 0.5 |
Probability both are girls =1/3.
Assumptions and limits
- Child sexes are independent and share the supplied girl probability.
- The family is known to have at least one girl, with no day or child-selection bias.
- Biological sex, gender identity, twins, and reporting selection are not modeled.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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