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to be mixed; to be blended with; to be combined
to associate with; to mingle with; to interest; to join
「混じる」 has another reading with different meanings.
さまざまな色が混じり合った絵を描いた。
I painted a picture with various colors mixed together.
大勢の人が混じるパーティーに行った。
I went to a party with many people mixed in.
その意見には賛否が混じっている。
The opinion is mixed with pros and cons.