Basic concepts of probability distribution

What this specific question is asking

Most wrong answers here are setup errors, not math errors. Confirm favorable outcomes and total outcomes — units, periods and definitions — before you touch Probability Calculator, and keep the output's unit attached when you use it.

Use the example (Worked example: The chance of rolling a 6 on a fa shows the expected scale for typical inputs. Use your result the same way: as one checked input into the decision, not the whole decision. Read the magnitude before the decimals: a result ten times too large or small almost always means a unit or period slipped, not that the formula failed.

Before trusting any figure from a calculator, fix the basis: the units each input is in, the period each rate or count covers, and the convention the formula assumes. Two calculators can disagree by a few percent purely because one rounds monthly and the other compounds daily, so write down which convention you are using before comparing answers across tools.

A worked example is a calibration run, not a target: reproduce it exactly first, then change one input at a time and watch the output move. If the output does not move when an input changes, the input is not wired the way you think — check the field labels and units before the arithmetic.

If two sources disagree on this figure, prefer the one that states its method. This page states its method next to every result, and the worked example above can be reproduced by hand in a minute — that reproducibility is the check. For money, health or construction numbers, finish by confirming against the authoritative source or a professional, since fees, taxes, tolerances and rounding at each step move the real-world answer.

One last habit separates a quick answer from a reliable one: write down what you expected before you run the check. When the result matches your expectation, you have a number and a reason; when it does not, you have found the assumption to fix first — before any tool output gets trusted.