Réponse :
A = 3/7 + 4/21 - 5/2
A = 18/42 - 8/42 - 105/42
A = 95/42
B = 2/3 - 4/3 x 5 /2
B = 2/3 - 20/6
B = 4/6 - 20 /6 = - 16 /6 = - 8 /3
C = 5 + ( 1 + 1/8) : 3/4
C = 5 + ( 8/8 + 1/8) : 3/4
C = 5 + 9 /8 : 3/4
C = 5 + 9/8 x 4/3
C = 5 + 36/24
C = 5 + 3/2
C = 10/2 + 3/2 = 12/2 = 6