The fifth rule - Addition of basic symbols in additive notation in a Roman numeral

Numerals addition rule in additive notation:

A numeral placed immediately after another one of a larger or equal value (next to the right of it), is added to the latter. This is called additive notation.

This rule outweigh the third rule, that of subtraction in subtractive notation when writing Roman numerals.

Only when a number can't be built by following the addition rule in additive notation, the subtractive notation applies.

Also remember the rule no. 2, of repetition (numerals may not occur more than three times in a row in any numeral).

Example:

Number two (2) is written using a single symbol listed under the first rule: I (1). Placing the I symbol after another I leads to: II (2);

Number three (3) is also written by placing I after I (1) twice, so we get: III (3);

Number six (6) is written by placing I (1) after V (5), so we get: VI (6);

Number seven (7) is written by placing I (1) after V (5) twice, so we get: VII (7);

Number eight (8) is written by placing I (1) after V (5) three times: VIII (8) - not IIX;

Number eleven (11) is written by adding I (1) to X (10), by placing I (1) after X (10): 11 = 10 + 1 = X + I = XI;

Number twenty (20) is written by placing X (10) after another X (10): 20 = 10 + 10 = X + X = XX;

Number one hundred four (104) is written by placing IV (4) after C (100), to get 104 = 100 + 4 = C + IV = CIV.