What is the total number of regions where the average family size is 2.8?
CREATE TABLE "table1_16048129_5" (
  "region_of_ussr" text,
  "number_of_families" real,
  "number_of_people" real,
  "average_family_size" text,
  "pct_of_total_deportees" text
);
SELECT COUNT("pct_of_total_deportees") FROM "table1_16048129_5" WHERE "average_family_size"='2.8';