Bonjour,
15/20 - 2/8
= 3/4 - 1/4
= 2/4
= 1/2
49/35 + 9/15
= 7/5 + 3/5
= 10/5
= 2
25/8 - 27/24 +11/11
= 25/8 - 9/8 + 11/11
= 16/8 + 11/11
= 2+1
= 3
26/48 + 11/24
= 13/24 +11/24
= 25/24
14/12 -25/30
= 7/6 - 5/6
= 2/6
= 1/3
12/12 -15/30 +9/6
= 6/6 - 3/6 +9/6
12/6
= 12/6
= 2