CREATE TABLE table_36392 ("Date" TEXT, "Visitor" TEXT, "Score" TEXT, "Home" TEXT, "Decision" TEXT, "Attendance" FLOAT, "Series" TEXT)

How many Attendances that has a Visitor of philadelphia on may 20?
SELECT AVG("Attendance") FROM table_36392 WHERE "Visitor" = 'philadelphia' AND "Date" = 'may 20'
SELECT AVG("Attendance") FROM "table_36392" WHERE "Date" = 'may 20' AND "Visitor" = 'philadelphia'