Bonjour

C = 2/5 + 3/7

C = (2 x 7) / (5 x 7) + (3 x 5) / (7 x 5)

C = 14/35 + 15/35

C = 29/35

D = 5/2 x 7/35

D = 35/70

D = (35 x 1) / (35 x 2)

D = 1/2

E = 2/3 : 4/5

E = 2/3 x 5/4

E = 10/12

E = (2 x 5) / (2 x 6)

E = 5/6.