Answer:
   
   Note that the requirements for a minyan are not biblical in origin.
   The reasons are rabbinic. The following are some sources:
     * M Megillah 4:3 and BT. Meg. 23b list the required occasions for a
       minyan: the sheva berakhot at a wedding; the chazarat ha-shatz of
       the Amidah; the reading of Torah from the scroll and of Haftarah;
       the kedusha (derived from Lev. 22:32, ve-nikdashti betokh benei
       yisra'el, matching the word tokh with Num. 16:21, mitokh ha-edah,
       where the context makes it clear that sanctification requires a
       public.
     * The number 10 is derived from Num. 14:27, where the ten spies
       opposing the invasion were called an edah ra'ah. There were also
       other derivations, one of them being the "ten righteous people"
       that were lacking in Sodom.
     * Soferim 10:7 adds Kaddish and barekhu to the rubrics requiring a
       minyan, though here, the plain text would suggest that the minyan
       could be seven (or even six) worshippers, after the number of
       words in Judges 5:2. But later interpretation favored the reading
       of this prescription as signifying that the numbers six or seven
       refer to persons who, within a regular minyan of ten men, have not
       heard the Kaddish or barekhu. If we read the Soferim passage
       plainly it appears that the author(s), writing in Palestine, meant
       to deal with situations when it was difficult to gather a minyan.
     * The Talmud (YT Meg. 4:4 and Ber. 7:3 ) provides that if a minyan
       was present to start with, but some people had left afterwards,
       the service could conclude as if they were still present, provided
       that the majority remain (so Rambam, Yad, Tefillah 8:8, Sh. A. O.
       H, 55:4; and the Hafetz Chayim, Mishnah Berurah, # 24).
       
   Note: If one cannot scrape up 10 minyan-qualified individuals
   (traditional Judaism only accepts adult men; Reform also accepts adult
   women), one can count the Torah as part of the Minyan. One can also
   count a minor holding a chumash, as long as the group looks like it
   could be 10 until you bother counting them. This is based on Tractate
   Berachos 47b. The source is that Abraham first begged G-d to save
   Sodom, Gemorra and 3 smaller towns if they had 50 people. He then fell
   back to 45. Apparantly, therefore, if you can't get 10 per city, you
   can rely on 9. But this is only if you can not possibly scrape up 10.