CREATE TABLE table_55150 ("Home team" TEXT, "Home team score" TEXT, "Away team" TEXT, "Away team score" TEXT, "Venue" TEXT, "Crowd" FLOAT, "Date" TEXT)

What is the average crowd size at Princes Park?
SELECT SUM("Crowd") FROM table_55150 WHERE "Venue" = 'princes park'
SELECT SUM("Crowd") FROM "table_55150" WHERE "Venue" = 'princes park'