a. 9/8 = .../24
9/8 = (9*3)/(8*3) = 27/24
9/8>25/24 car 27/24>25/24
b. 11/4 et 23/8
11/4 = (11*2)/(4/2) = 22/8
Donc 11/4<23/8
49/42 et 8/7
8/7 = (8*6)/(7*6) = 48/42
Donc 49/42>8/7
55/32 et 7/4
7/4 = (7*8)/(4*8) = 56/32
Donc 55/32<7/4
Voilà j'espère que tu as compris ! ^^