Réponse:

a) 3/10 + 7/8 = 3×4/10×4 + 7×5/8×5 = 12/40 + 35/40 = 47/40

b) 5/8 + 7/12 = 5×3/8×3 + 7×2/12×2 = 15/24 + 14/24 = 29/24

c) 11/6 + 5/21 = 11×7/6×7 + 5×2/21×2 = 77/42 + 10/42 = 87/42

d) 2/9 + 1/21 = 2×7/9×7 - 1×3/21×3 = 14/63 - 3/63 = 11/63

e) 11/15 - 4/25 = 11×5/15×5 - 4×3/25×3 = 55/75 - 13/75 = 42/75

f)13/14 - 9/35 = 13×5/14×5 - 9×2/35×2 = 65/70 - 18/70 = 47/70

Explications étape par étape:

/ représente la bar de fraction