Probability Calculator
Compute single-event probability with odds, or combined probabilities of two independent events.
Probability Calculator
Compute single-event probability with odds, or combined probabilities of two independent events.
How to use the Probability Calculator
- Choose "Single event" or "Two independent events".
- Enter the values.
- Click Calculate.
Formula
Single: P = favorable / total
Two independent: P(A and B) = P(A) × P(B)
P(A or B) = P(A) + P(B) − P(A and B)
Example
Single: 3 favorable out of 10 total. P = 3/10 = 0.3 = 30%.
Step-by-step calculation
- Favorable outcomes: 3.
- Total outcomes: 10.
- Probability = 3 ÷ 10 = 0.3.
- Expressed as 30% or odds 3:7.
Real-world uses
- Risk assessment.
- Game theory and strategy.
- Quality control sampling.
Common mistakes
- Assuming all outcomes are equally likely.
- Confusing "and" (multiply) with "or" (add).
- Double-counting overlapping outcomes.
Frequently asked questions
What are odds?
Odds in favor = favorable:unfavorable. For P=30%, odds are 3:7.
When do I multiply vs add?
Multiply for "and" (both events). Add for "or" (at least one), subtracting overlap.
Can probability exceed 100%?
No. Probability is always between 0 (impossible) and 1 (certain).