Category
Probability & Counting calculators
Counting and probability reward careful reading more than heavy algebra. The key questions are always the same: does order matter, and can items repeat?
These tools make you answer those two questions explicitly, then show the formula that follows. Counting results use exact whole-number arithmetic, so large answers are not rounded.
All probability & counting tools
What you can do here
- Count arrangements and selections
- Work out the chance of one event, of both, or of either
- Check a probability worksheet
- See how fast counts grow as n increases
Learn the method first
Guides in this category teach the idea, then hand you to the matching calculator to practise.
- Permutations vs Combinations: How to Choose the Right One
- Probability Basics: One Event, “And” and “Or”
Questions about this category
How do I know whether to use a permutation or a combination?
Ask whether swapping two chosen items gives a different outcome. If yes (race places), use a permutation. If no (a committee), use a combination.