Riot, Why Do I Have Plat 5 Players On My Team In Plat 1 - Diamond 5 Elo?
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A plat 5 jungler, with plat 3 mmr, is able to play with Plat 1/Diamond 5 players with Diamond mmr. Note the plat 5 jungler has a 55% winrate of his past 20 games, there is no reason he should be anywhere near plat 1 mmr with that winrate.