Casos equiprobables
Simple probability
Divide favorable outcomes by all possible outcomes. Before using it, confirm that every outcome has the same probability.
Probability and Statistics
Probability calculator
Calculate a probability and understand what it means, how it was obtained and whether the entered data is consistent.
What do you want to calculate?
Choose a mode. Only the inputs needed for that operation will appear.
Publicidad
What each mode calculates
The words “or,” “and” and “given” represent different operations.
A o B
Union
Add P(A) and P(B), but subtract their overlap to avoid counting it twice.
A y B
Intersection
If the events are independent, multiply their probabilities. Otherwise, you need a conditional probability.
No A
Complemento
Subtract P(A) from 1. The result contains all outcomes where A does not occur.
A dado B
Condicional
Restrict the reference space to outcomes where B has already occurred.
Diferencia clave
Independientes no significa excluyentes
Independent events can occur together. Mutually exclusive events have an intersection of zero.
Fraction, decimal and percentage
All three forms express the same proportion. For example, 1/4 es 0.25 and also 25%. The calculator preserves internal precision and rounds only the display.
Related calculators
Frequently asked questions
How do you calculate a simple probability?
When all outcomes are equally likely, divide favorable outcomes by possible outcomes. For example, rolling an even number on a fair die has 3 favorable outcomes out of 6: 3/6 = 1/2 = 50%.
When can I divide favorable outcomes by possible outcomes?
Only when the elementary outcomes have the same probability. It works with a fair coin or die, but simply counting outcomes is not enough when some have different weights.
What does P(A or B) mean?
It is the union: A occurs, B occurs or both occur. If they can overlap, subtract the intersection to avoid counting it twice.
What does P(A and B) mean?
It is the intersection: both events occur. If they are independent, multiply P(A) and P(B); if they are dependent, you need conditional information.
What is the difference between independent and mutually exclusive events?
Independent events do not change each other's probabilities and can overlap. Mutually exclusive events cannot occur together, so their intersection is zero.
What is conditional probability?
P(A | B) measures the probability of A within the outcomes where B has already occurred. Divide P(A and B) by P(B), provided P(B) is greater than zero.
How do I convert between fraction, decimal and percentage?
Divide a fraction to obtain the decimal; multiply the decimal by 100 to obtain the percentage. For example, 1/4 = 0.25 = 25%.