J'ai besoin d'aide pour cette exercice .

1. A = 8/3 - 5/3 : 20/21
A = 8/3 - 5/3 x 21/20
A = 8/3 -  (5x21)/(3x20) or 21 = 3x7 et 20 = 4x5
A = 8/3 - (5x3x7)/(3x4x5)
A = 8/3 - (15x7)/(15x4)
on simplifie par 15
A = 8/3 - 7/4
A = (8x4)/(3x4) - (7x3)/(4x3)
A = 32/12 - 21/12
A = (32-21)/12
A = 11/12

2. B = (2+2/3) : (4/5 - 2/3)
B = ([2x3]/3+2/3) : ([4x3]/[5x3] - [2x5]/[3x5])
B = (6/3+2/3) : (12/15 - 10/15)
B = ([6+2]/3) :([12-10]/15)
B = 8/3 : 2/15
B = 8/3 x 15/2
B = (8x15)/(3x2) or 8 = 2x4 et 15 = 3x5
B = (2x4x3x5)/6 or 2x3 = 6 et 4x5 = 20
B = (6 x 20)/6
On simplifie par 6
B = 20