Ordinal numbers are first, second, third, etc.

primero – first
segundo – second
tercero – third
cuarto – fourth
quinto – fifth
sexto – sixth
séptimo – seventh
octavo – eighth
noveno – ninth
décimo – tenth

Beyond tenth cardinal numbers (one, two, three etc.) should be used instead of ordinal numbers to simplify matters: once – eleventh, doce – twelfth etc.

However, there is a more complicated method of expressing the ordinal number system, but we don’t advise you to use it. For example, eleventh is undécimo, twelfth is dudécimo. For numbers 13-19 put décimo in front of the ordinal numbers 3-9: decimotercero (13th) or decimocuarto (14th) etc.

Some of the the ordinal numbers are:
vigésimo – twentieth
trigísimo – thirtieth
cuadragésimo – fortieth
quincuagésimo – fiftieth
sexagésimo – sixtieth
septuagésimo – seventieth
octogésimo – eightieth
nonagésimo – ninetieth
centésimo – hundredth

Tiquismo (Costa Rican expression) of the week:  Estar  sobre la jugada  means to be on top of things.