Numbers in the teens, twenties and thirties follow the same form as the first set, only with X's indiing the number of tens. So XXXI is 31, and XXIV is 24. L: L means 50. Based on what you've learned, I bet you can figure out what 40 is. If you guessed XL, you're right = 10 subtracted from 50. And thus 60, 70, and 80 are LX, LXX and LXXX. C: C stands for centum, the Latin .