It sometimes happens that a group of men forms to make a Minyan, but as they do not have ten men, they ask several men who have already prayed to join them so they have a Minyan. What is the minimum required number of men who have not previously prayed, to allow reciting the Hazara (repetition of the Amida)?
The Halachic authorities rule (based on the Hida’s ruling in Kesher Gudal, 18:4) that the Hazara may be recited if there are nine men answering "Amen" to the Hazan’s blessings, at least six of whom had not prayed previously. The Hazara may be recited if four of the ten men in attendance had prayed previously, but not if five or more have previously prayed, such that only five men or less are currently praying. As long as at least nine men are listening to the Hazara and answering "Amen," and there are at least six men who are now praying, the Hazara may be recited. It must be emphasized that only nine men are required in addition to the Hazan; it is not necessary for there to be ten men in addition to the Hazan for the Hazara to be recited.
Summary: The repetition of the Amida may be recited if there are least nine men listening and answering "Amen," at least six of whom had not prayed previously.