Probability Tree Calculator

This calculator multiplies together the probabilities of up to four independent branches to get Combined Probability, then derives Complement and At Least One Success from it. Branch 3 and Branch 4 are optional: the engine only folds them into the tree when their value is strictly greater than 0 (activeBranches.push(branch3Prob) only runs "if (branch3Prob > 0)", line 12), so with both left at their default of 0, Combined Probability is just Branch 1 × Branch 2 — a two-branch tree, not a four-branch one. Because Combined Probability is a plain product, Branch 1 and Branch 2 move it by exactly the same proportional amount at any shared value, including the calculator's defaults of 0.5 each.

Total Entropy sums the binary entropy of each active branch, and at the default 0.5 for both branches, a proportional nudge shows zero net effect — not because entropy is flat there, but because 0.5 sits exactly at the peak of the binary entropy curve, which is symmetric around p = 0.5 (entropy at 0.55 equals entropy at 0.45), so the calculator's paired up/down probe cancels out exactly at that specific point. Away from p = 0.5, entropy does change with branch probability. The calculator does not account for dependent or conditional branches: combinedProb is a flat product of the entered probabilities (activeBranches.reduce((acc, p) => acc * p, 1), line 18), which is only correct when the branches are genuinely independent — a real tree where a later branch's probability depends on an earlier one's outcome is outside this model.