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Calcimator

Probability Tree Calculator

Calculate sequential and combined probabilities for multi-stage probability trees with up to 4 branches.

Inputs

Results

Combined Probability

0.25

At Least One Success

0.75

Complement (not all)0.75
Active Branches2
Total Paths4
Expected Successes1
Total Entropy (bits)2
How to Use This Calculator
  1. Enter the number of branches at each node of the probability tree.
  2. Input the probability for each branch at each level (probabilities at each node must sum to 1).
  3. Label each leaf node with its outcome.
  4. Review the probability of each path and combined outcome probability.
  5. Sum leaf probabilities for a given outcome to calculate its total probability using the law of total probability.

How the result changes with Branch 1 Probability

Branch 1 ProbabilityCombined ProbabilityAt Least One Success
0.10.050.55
0.350.1750.675
0.650.3250.825
0.90.450.95

What each input means

Branch 1 Probability
Probability of the first event occurring (0 to 1)
Branch 2 Probability
Probability of the second event (conditional on first if sequential)
Branch 3 Probability (0 = skip)
Set to 0 to exclude this branch from the tree

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Branch 1 Probability = 0.5, Branch 2 Probability = 0.5, Branch 3 Probability (0 = skip) = 0, Branch 4 Probability (0 = skip) = 0 = 4 input(s) provided
  2. Calculate Combined Probability
    0.25 = 0.25
  3. Calculate At Least One Success
    At Least One Success
    0.75 = 0.75
  4. Calculate Complement
    Complement
    0.75 = 0.75
  5. Calculate Active Branches
    Active Branches
    2 = 2

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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