21 in Roman numerals, how to write?

21 = XXI
20 = ? ... 22 = ?
Explanations below.

Roman numerals used to make the conversion:


I = 1; X = 10;

Reading rules

1. Break the number (decompose it) into place value subgroups:

21 = 20 + 1;

2. Convert each subgroup:

20 = 10 + 10 = X + X = XX;
1 = I;

3. Wrap up the Roman numeral:

21 = 20 + 1 = XX + I = XXI;

Final answer:


21 = XXI

In Roman numerals, how to write:
20 = ? ... 22 = ?

In Roman numerals online converter

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Roman numerals reading rules, summary: