CREATE TABLE table_47913 ("Rider" TEXT, "Manufacturer" TEXT, "Laps" FLOAT, "Time" TEXT, "Grid" FLOAT)

Can you tell me the sum of Grid that has the Manufacturer of aprilia, and the sandro cortese?
SELECT SUM("Grid") FROM table_47913 WHERE "Manufacturer" = 'aprilia' AND "Rider" = 'sandro cortese'
SELECT SUM("Grid") FROM "table_47913" WHERE "Manufacturer" = 'aprilia' AND "Rider" = 'sandro cortese'