SELECT MIN("Average") FROM table_48869 WHERE "Team" = 'beijing guo''an' AND "Games" > '240'
What is the smallest average for Beijing Guo'an when they played more than 240 games?
CREATE TABLE table_48869 (
    "Season" real,
    "Total Attendance" real,
    "Games" real,
    "Average" real,
    "High avg." real,
    "Team" text,
    "No. Of Clubs" real
)