Legit question about duo matchmaking

So, I remember reading a while ago that duo's in solo/duo ranked queue had higher winrate than solo, and Riot did something to make it more fair by making games harder for duo.

Now, my question is, how does this work?

Say the summoners who duo are both gold.

1. Are the duo matched with lower elo (say, silver teammates) against high elo (e.g. platinum ?)

2. Are the duo matched with and against higher elo (plat teammates, plat enemy?)

Thanks... =)