I've learned the case endings for informal language eg. 7th case pl. - ama, 6th case pl. ach, masc. ej, neutral y and so on, however I'd like to know how commonly each is used in informal Czech, for example it seems to me that ama and y for neutral adjectives are used more often than ach for locative plural and ej for masculine inanimate adjectives. For example - Pred dvema tydnama (not tydny) Vidim dve maly okna (not mala okna) Muj pocitac je drahej (not drahy) Je tam cerveny auto (not cervene auto) Kazdy den hodne lidi seda v vlakach (not vlacich) How common are all of these and others in informal situations? How informal does the situation have to be? Are some very informal and others less? I'd really appreciate any opinions on this because often I'm never really sure which form is appropriate when I'm speaking.