Learn Russian: Люди часто спорят о чужих деньгах. - People often argue about other people's money.

The preposition о (about) always requires the Prepositional case. The word for money, деньги, is always plural in Russian. In the Prepositional plural, nouns usually take the ending -ах (or -ях). So, деньги becomes деньгах.

Why does чужих end in -их instead of -ых for a plural adjective?

Чужих comes from the adjective чужой (someone else's). Normally, plural adjectives take -ых in the Prepositional case. However, the Russian spelling rules say you can never write the letter ы after ж, ш, ч, щ, г, к, or х. Since the stem ends in ж, we must use -их instead.

How exactly does чужих translate to "other people's"?

The adjective чужой means "belonging to a stranger", "foreign", or "alien". Russian does not have a direct word-for-word equivalent to the English phrase "other people's", so it uses чужой to describe anything that belongs to someone else.

Why does the verb спорят end in -ят?