CREATE TABLE table_18808 ("Rank by average" FLOAT, "Competition finish" FLOAT, "Couple" TEXT, "Total" FLOAT, "Number of dances" FLOAT, "Average" TEXT)

tell the mean of the times competition for the 7 jigs
SELECT "Rank by average" FROM table_18808 WHERE "Number of dances" = '7'
SELECT "Rank by average" FROM "table_18808" WHERE "Number of dances" = '7'