Everyone knows that arithmetic is true: 2 + 2 = 4. But surprisingly, we don’t know why it’s true. By stepping outside the box of our usual way of thinking about numbers, my colleagues and I have ...

A key part—though surely not the only part—of early-grades math is ensuring students get the basic arithmetic functions down and, beyond that, making sure they’re able to swiftly and automatically ...

Most famous equation: Einstein's E = mc2, which means energy is equal to mass times the speed of light squared. Known digits of pi: More than 105 trillion digits Digits of pi NASA uses for equations: ...