Numbers following names of kings, etc., are ordinal up to the tenth; then generally cardinal, as—
Felipe II. (segundo): Philip II.
Alfonso XIII. (trece): Alphonso XIII.
Fractional numbers up to 1/10th are the same as ordinal numbers, except—
(Un) medio: one half.
Un tercio (not tercero): one-third.
From 1/11th upwards, fractions are formed from cardinal numbers adding to them the termination =avo=, as—
Un dieciseisavo[65]: 1/16.
Un need not be used before the fractions 1/2, 1/3 and 1/4, preceded by an integer, as—
Uno y cuarto: One and a quarter.
Cuatro y tercio: Four and a third.
La mitad: The half.
La tercera parte: The 3rd part.
La cuarta parte: The 4th part.
La duodécima parte: The 12th part.
[Footnote 65: If the cardinal number ends in a vowel, this is elided, as veinte—un veintavo (1/20th). If it ends in ce the c is changed into z as, doce—un dozavo (1/12th).]
Collective Numbers.