halacha - Agnostic Jew serving as the tenth for a minyan

I remember reading a responsum on the issue of agnostic Jew's serving as the tenth for a minyan, but do not remember the outcome. Does anyone know the rule?

Also, do we count, as the tenth man, a tinok shenishbah and one who does not understand the prayers at all?

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  If it is permitted, would it be different for a lower level of chiyuve (obligation) for a minyan such as Maariv?

  
  


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  If it is forbidden, would it be different for a higher level of chiyuve for a minyan such as Zimun, or someone who has a chiyuve for kaddish.

  
  

Answer

Sam gave this source in a comment last year, but no-one ever came to post an answer, so i'll do that now...

In Igrot Moshe OC 1:23, he paskens that בשעת הדחק - in an emergency, someone who is publicly Mechallel Shabbat can be counted for a minyan, to say Barchu, Kadish, and Kedusha. However, for Torah reading, it is more important to have 10 religious Jews.