The numbers 15 to 21 in roman numerals
The right column shows how each roman numeral adds up to the total.
| 15 | = | XV | = | 10 + 5 |
| 16 | = | XVI | = | 10 + 5 + 1 |
| 17 | = | XVII | = | 10 + 5 + 1 + 1 |
| 18 | = | XVIII | = | 10 + 5 + 1 + 1 + 1 |
| 19 | = | XIX | = | 10 + 10 − 1 |
| 20 | = | XX | = | 10 + 10 |
| 21 | = | XXI | = | 10 + 10 + 1 |