CREATE TABLE table_74650 ("Rank" TEXT, "County" TEXT, "Population  ( 1960 ) " FLOAT, "Population  ( 2000 ) " FLOAT, "Population  ( 2040 ) " FLOAT)

What was Oslo's population in 1960, with a population of 507,467 in 2000?
SELECT AVG("Population (1960)") FROM table_74650 WHERE "County" = 'oslo' AND "Population (2000)" > '507,467'
SELECT AVG("Population (1960)") FROM "table_74650" WHERE "County" = 'oslo' AND "Population (2000)" > '507,467'