bonjour aidée moi pour l'ex 90 et 91 svp

90)
1) 7/7 - 4/7 = 3/7
Le lundi soir il reste 3/7 du livre à Paul

3/7 x 2/3 = 6/21 = 3 x 2 / 3 x 7 = 2/7
Le mardi, Paul a lu 2/7 du livre

2) 7/7 - (4/7 + 2/7) = 7/7 - 6/7 = 1/7
Il restera encore à lire 1/7 du livre

91)
A = 1/2 + 3/2 x 7/3
A = 1/2 + 21/6
A = 1 x 3 / 2 x 3 + 21/6
A = 3/6 + 21/6
A = 24/6
A = 6 x 4 / 6 x 1
A = 4

B = (1/2 + 3/2) x 7/3
B = 4/2 x 7/3
B = 28/6
B = 2 x 14 / 2 x 3
B = 14/3

C = 20/9 - 5/3 x 2/3
C = 20/9 - 10/6
C = 20 x 2 / 9 x 2 - 10 x 3 / 6 x 3
C = 40/18 - 30/18
C = 10/18
C = 2 x 5 / 2 x 9
C = 5/9

D = (20/9 - 5/3) x 2/3
D = (20/9 - 5 x 3 / 3 x 3) x 2/3
D = (20/9 - 15/9) x 2/3
D = 5/9 x 2/3
D = 10/27