CREATE TABLE table_21312959_1 (no_in_season VARCHAR2, us_viewers__millions_ VARCHAR2)

How many episodes had the us viewers (millions) figure of 5.0?
SELECT COUNT(no_in_season) FROM table_21312959_1 WHERE us_viewers__millions_ = "5.0"
SELECT COUNT("no_in_season") FROM "table_21312959_1" WHERE "5.0" = "us_viewers__millions_"