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Basic probability is simply the number of favorable outcomes divided by the total number of possible outcomes — but it helps to see that result in percentage, decimal, and simplified fraction form all at once.
This calculator finds the probability of an event from favorable and total outcome counts, in all three common formats.
How it works
Enter the number of favorable outcomes and the total number of possible outcomes. The calculator divides favorable by total for the decimal and percentage forms, and uses the greatest common divisor to reduce the fraction to its simplest form.
- Enter favorable outcomes.
- Enter total possible outcomes.
- Click Calculate to see your results.
Examples
Drawing an ace from a deck
With 4 favorable outcomes (aces) out of 52 total cards, the probability is about 7.69%, or 0.0769 as a decimal, simplified to the fraction 1/13.
Who should use it
- Solving basic probability problems for coursework.
- Quick probability estimates for games of chance or simple random events.
Industry applications
- Mathematics and statistics education
- Game design and gambling odds
Advantages
- Shows the same probability in three commonly needed formats at once.
- Automatically simplifies the fraction to lowest terms.
Limitations
- Only handles simple, single-event probability with equally likely outcomes.
Common mistakes to avoid
- Confusing "favorable outcomes" with the total count of a specific category when outcomes aren't equally likely — this calculator assumes equally likely outcomes.
- Forgetting that probability must be between 0 and 1 (or 0% and 100%) — favorable outcomes can't exceed total outcomes.
Best practices
- Make sure your total outcomes count reflects the full, exhaustive sample space, not just a subset, or the probability will be understated.
Tips
- Remember that probability only applies cleanly when every outcome in your total count is equally likely — weighted or biased outcomes need a different approach.