Divide favorable outcomes by total equally likely outcomes. Formula and event probability remain visible in one place for independent verification.
For a finite equally likely sample space, event probability is favorable outcomes divided by all possible outcomes. The result lies from zero through one.
In basic probability, the relationship among the quantities matters just as much as their arithmetic.
Define nonoverlapping elementary outcomes, count the complete sample space, count those satisfying the event, and divide.
Seven favorable outcomes among twenty equally likely possibilities give 7/20=0.35, or 35%. This Basic Probability example can be compared with observed frequency.
This model handles fair dice, shuffled cards, random selections, and other settings where each elementary outcome has equal weight.
Counting alone is insufficient when outcomes have unequal probabilities. Favorable outcomes cannot exceed the total and the sample space cannot be empty. If the Basic Probability assumptions do not fit, consider opposite event.
An impossible event probability sign or magnitude usually points to field assignment before it points to rounding.
The input labels—favorable outcomes and total outcomes—encode the model used on this page. Write those labels beside source values when transferring a problem from paper or a spreadsheet. That small step catches transposed quantities and mixed units before they become a polished-looking event probability.
Adding favorable outcomes raises probability only if the total is held fixed; expanding the sample space can move the ratio differently. A one-field trial makes this relationship visible without reworking the entire example.
Choose rounding after considering how the result will be used. Comparison may need only a few significant digits, while a later multi-step calculation benefits from carrying more. In either case, retain the page's formula with the event probability so the underlying definition remains visible.
Empirical probability uses observed frequency rather than a theoretical equally likely outcome count. The distinction determines whether this page fits the original question.
If the number moves into a spreadsheet, give its cell a event probability heading and retain the source values favorable outcomes and total outcomes nearby. Context matters more than extra displayed digits.
A reproducible Basic Probability record contains Favorable outcomes, Total outcomes, the selected calculation mode, and the final rounding rule. Keep decimals on the zero-to-one scale during probability arithmetic and label any percentage conversion separately. Exact counting results should remain integers even when they are very large.
For Basic Probability, for an independent check, simplify the setup by removing one stage or fixing one object. The smaller result should relate to the original through a known factor, coefficient, or complement rather than through coincidence.
Yes for this counting ratio.
No.
The event is impossible within the stated model.
Multiply the decimal probability by 100.