MihsabaHow to use
This probability calculator keeps four common problem types separate: a single event from equally likely outcomes, two independent events, combinations and permutations, and binomial probability for a number of successes. Choosing the correct model matters more than simply entering numbers.
- Choose the problem type from the mode selector.
- Enter only the fields for that mode; probabilities accept forms such as 0.25, 25%, or 1/4.
- Calculate and read the outputs together with the independence warning for the two-event mode.
How it is calculated
Example
Example: rolling a 6 on a fair die gives 1/6 ≈ 16.67%, with a complement of about 83.33%. For counting, choosing 3 items from 10 without order gives C(10,3)=120, while arranging 3 from 10 gives P(10,3)=720.
Important notes
The simple-event ratio assumes elementary outcomes are equally likely. In this tool, P(A and B)=P(A)P(B) and the corresponding OR rule apply only to independent events. The binomial model assumes a fixed number of independent trials, constant success probability and two outcomes per trial. Use another model when those assumptions do not hold.
Frequently asked questions
When should I use combinations instead of permutations?
Use combinations when order does not matter and permutations when changing order creates a different outcome.
Is P(A or B) always just the sum?
No. The intersection must be subtracted to avoid double counting; this calculator obtains that intersection by multiplication only under independence.
What are the binomial assumptions?
A fixed number of trials, independent trials, a constant success probability and two outcome classes per trial.
Is this calculator free?
Yes. It is free to use and requires no account.