You may never have heard of modular arithmetic, but you use it every day without the slightest difficulty. In this system, numbers wrap around when they reach a certain size called the modulus ...

We use modular arithmetic all the time ... It's called Zeller's formula and here it is: Let's do some examples. I'll pick a date we know: December 7, 1941 was a Sunday. The corresponding numbers ...

I now know that this is actually a part of math called modular arithmetic. Sometimes it’s informally called clock arithmetic, because it’s like how we tell the time: When we get around to 12 ...