Quote Originally Posted by lenssideways8 View Post
Some examples of the construction being used . . .

билет на одну поездку (ticket for one trip)
билет на две поездки (ticket for two trips)
билет на пять поездок (ticket for five trips)

Why in the example for five trips is поездка in the genitive? First two are accusative, then it switches to genitive. Is this correct? Any help is appreciated.
Let me continue 
So, the trick is as follows:
(1) In collocations «один/одна/одно + a noun» the two parts (a numeral and a noun) fully agree. It means that when you decline, you decline the whole collocation. I would even say that a noun prevails in this collocation – we manipulate a NOUN (not a numeral), while the numeral obeys the noun (like an indefinite article). For example, you can omit the numeral from the collocations «одна поездка, на одну поездку, одной поездкой, без одной поездки, об одной поездке» without any harm to the meaning: «поездка, на поездку, поездкой, без поездки, о поездке».
Further we’ll talk ONLY about the numerals in the Nominative and Accusative case-forms and their collocation with inanimate nouns:
(2) In collocations «пол-, 2, 3 and 4 + a noun» we use a noun in the form which, surprisingly, coincides with the GENITIVE case-form SINGULAR (половина/две/три/четыре + поездки/цены/билета). The noun form remains the same, e.g. «половина/две/три/четыре поездкИ» (Nominative numeral), «на половину/две/три/четыре поездкИ» (Accusative numeral).
(3) In collocations «5, 6… + a noun» we use a noun in the GENITIVE case-fom PLURAL. It refers both to the Nominative and Accusative, e.g. «пять/шесть/семь… поездОК» (Nominative numeral), «на пять/шесть/семь… поездОК» (Accusative numeral).