Bonjour
A = 4/3 - 1/3 = 3/3 = 1
B = - 5/4 + 3/20
B = (- 5 x 5) / (4 x 5) + 3/20
B = - 25/20 + 3/20
B = - 22/20
B = (2 x - 11) / (2 x 10)
B = - 11/10.
C = - 8/5 + 4/3
C = (- 8 x 3) / (5 x 3) + (4 x 5) / (3 x 5)
C = - 24/15 + 20/15
C = - 4/15
D = 21/6 x 15/14
D = 315/84
D = (21 x 15) / (21 x 4)
D = 15/4
E = 7 - 4/3
E = (7 x 3) / (1 x 3) - 4/3
E = 21/3 - 4/3
E = 17/3
F = 10/18 : 35/18
F = 10/12 x 18/35
F = 180/420
F = (60 x 3) / (60 x 7)
F = 3/7.