Can someone explain?

I would like someone to explain to me why I'm silver 1 and keep facing players in gold v-plat v in ranked. In my prelims I went 6-4 and and got into silv 2, my first match I played with a lower rank buddy of mine and was placed against people my rank so I assume because my buddy was with me so I assume I was placed against people in the middle of me and him. After that, I started playing solo que and started noticing that I was getting placed with people a lot higher rank than I was. At first it they were gold v-gold 3 but now I'm getting placed against plat v more frequently than I was before, this makes it a lot harder for me to get lp as they have over 300+ games in ranked and probably twice as much in norms while I only have about 40 games worth of experience in ranked. http://www.lolking.net/summoner/na/58605720