1. Definition
The joint probability follows P(AB)=P(A)P(B|A); for independent events P(AB)=P(A)P(B).
2. Formula & Notation
| P(A) | Probability of A |
| P(B|A) | Conditional probability |
| P(AB) | Both occur |
3. Properties & Laws
- P(AB)=P(A)P(B|A);
- Independent: P(A)P(B);
- Extends by chaining;
- Relates to conditional probability.
4. Steps
- Enter P(A) and P(B|A);
- Click "Calculate";
- Or click "Load Example".
5. Worked Examples
Example: P(A)=0.5, P(B|A)=0.4.
Solution: P(AB)=0.2.
6. Common Pitfalls
Use P(A)P(B) only if independent;
P(B|A) differs from P(B);
Not the addition rule.