Chess.com uses a Glicko rating system. This system using a factor called RD, which stands for rating deviation. If you have a very high rating deviation, then your rating will be extremely volatile. If a player is new to the site, or hasn't played in a very long time, they will have a high RD and be able gain 200 pts by beating lower rated opponents.
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How does somebody win over 200 pts by beating two opponents rated lower than them?