How does ranked mm pick your teammates?

Generally speaking, if you are higher than average, you get paired with weaker teammates, and vice versa.

It tries to put you with people (or groups*) with a similar MMR to yours. I believe the system also takes number of games played into account to a degree as well, though that's not a hard and fast rule.

*Note on how group MMR works: If multiple people queue together, they get a group MMR that represents the group as a whole. I believe this MMR is the average MMR of the group as a whole, though there is a bit of a weighting factor added in depending on how many people are together, to account for the improved teamwork the group likely has (voice coms or just familiarity with one another). For example, if a 1300 MMR and 1500 MMR player queue together, their raw combined average would be 1400, but matchmaking would add some to that because they're queued together. They might wind up at, say, 1450.

ty for the replies guys.