Calculators & games

Play with the numbers yourself. Every tool runs in your browser and shows the arithmetic behind it.

Real or fake gameOne pattern is truly random, one was faked by a person. Coin flips, stars and dice: can you spot the real one? Birthday match calculatorHow many people before two share a birthday? Slide from 2 to 100 and watch it pass 50% at 23. Three doors gameThe switch-or-stay puzzle. Play by hand, then simulate 1,000 games. Lottery odds calculatorPowerball, Mega Millions, EuroMillions or your own rules, next to everyday risks.

Coming next

A queue simulator for the "why is my line always slower" question, and a false-positive calculator for medical tests. New tools land alongside the videos.