Most of us have little trouble working out how many milliliters are in 2.4 liters of water (it's 2,400). But the same can't be said when we're asked how many minutes are in 2.4 hours (it's 144).

A new collection of research papers examines how humans conceptualize numbers and the numeral systems we’ve build around them ...

Algebra uses letters to represent unknown values. Unknown values are commonly represented by the letters x and y. There are several principles you need to know to be able to use algebraic notation.