Probability Calculator
以下详细说明暂以英文提供。
The AND and OR rules
Two events combine under one key question: must both happen, or does either one count? For independent events, AND multiplies — rolling a six and flipping heads is (1/6) × (1/2) = 1/12, because the paths branch independently. OR adds but must subtract the overlap so it is not counted twice: P(A or B) = P(A) + P(B) − P(A and B). Equivalently, the four paths "A only", "B only", "both", and "neither" are mutually exclusive and sum to exactly 100%, which this calculator lists so you can trace every branch of the tree.
常见问题
What makes two events independent?
One occurring does not change the other’s probability. Separate dice, coins, or different people drawn one at a time with replacement are independent; cards drawn without replacement are not, since each draw shrinks the deck.
How is probability different from odds?
Probability compares favorable outcomes to all outcomes — 1/6 — while odds compare favorable to unfavorable: 1 to 5. The single-event tab shows both, plus the complement.