8 = eight 8th = eighth (achtste)
9 = nine 9th = ninth (negende)
10 = ten 10th = tenth (tiende)
20 = twenty 20th = twentieth (twintigste)
21 = twenty-one 21st = twenty-first (éénentwintigste)
30 = thirty 30th = thirtieth (dertigste)
31 = thirty-one 31st = thirty-first (éénendertigste)