Does one have to say Amen, Borchu, Kedushah while they are learning and there is a Minyan going on which one is not Davening with?

If one has already answered Kedushah but hears a Minyan saying Kedushah, he should stop and say it with them.

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This answer is sponsored:

לע”נ רב יונה בן רב מאיר ע”ה