Probability Addition Rule Calculator
Calculate probability addition rule with explicit inputs and a worked example.
Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
Example Calculation
- P(A): 0.5
- P(B): 0.4
- P(A and B): 0.2
P(A)=0.5, P(B)=0.4 and intersection 0.2 gives union 0.7.
Frequently asked questions
How do I use this calculator?
Enter p(a), p(b), p(a and b). The result updates automatically. Use Reset to restore the example values.
What method does it use?
P(A or B) = P(A)+P(B)−P(A and B). Follow the units and definitions shown with the inputs to apply this relationship consistently.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.