20 1/19-4 12/19-5 17/19 = 9 10/19

1) 20 1/19 - 4 12/19 = 16 - 11/19 = 15 19/19 -11/19 = 15 8/19

2) 15 8/19 - 5 17/19 = 10 - 9/19 = 9 19/19 -9/19 = 9 10/19