How does an onyx solo searching get a platinum teammate? i mean its not the guys fault and if he was partied up with the other people on my team why was i paired up with them 
There are Hidden Ranks which are more important than actual ranks, such as Onyx or Diamond. They are always constantly changing depending on how you do. If you do bad in a game because you are not warmed up, your rank will go down until you start doing better, and Vise-Versa. These ranks practically bypass actually ranks in the sense that if you get Bronze, but start playing like a Champion after 3-4 games, your hidden rank will skyrocket, allowing you to play with higher ranked players. This may be the case for you. If the player did bad that game, his hidden rank will drop down. Luke TheNerdable has a video on this, so watch that if you want an in-depth, factual explanation of your current situation. Hope I helped!
-TrueHero808
Head over to the Matchmaking section and read the pinned feedback threads. It explains quite a bit.