Addition Rule Calculator
🎲 Statistics & probability. Use the Addition rule (OR rule) formula to find p(a or b), p(a), p(b), p(a and b): pick the value you want, type the others, and the answer updates as you go.
Pick the ○ next to the value you want to find, fill in the others, and it solves as you type.
What each letter means
| Quantity | Unit |
|---|---|
| P(A or B) | no unit |
| P(A) | no unit |
| P(B) | no unit |
| P(A and B) | no unit |
Worked example
Find the p(a or b) when P(A) = 0.5, P(B) = 0.3, P(A and B) = 0.15.
Using P(A or B) = P(A) + P(B) - P(A and B): P(A or B) = 0.65.
Frequently asked questions
What is the formula for Addition rule (OR rule)?
P(A or B) = P(A) + P(B) - P(A and B).
What do the letters stand for, and what units are used?
P(A or B), P(A), P(B), P(A and B).
How do you calculate p(a or b)?
Put the values into P(A or B) = P(A) + P(B) - P(A and B). For example, with P(A) = 0.5, P(B) = 0.3, P(A and B) = 0.15, p(a or b) = 0.65.
Can I solve for a different value?
Yes. In the calculator above, pick the circle next to any value (p(a or b), p(a), p(b), p(a and b)) and fill in the others: it rearranges the formula for you.
