Bonsoir

12)

A = 7/2 + 5/6 - 5/3

A = (7 x 3) / (2 x 3) + 5/6 - (5 x 2) / (3 x 2)

A = 21/6 + 5/6 - 10/6

A = 16/6

A = (2 x 8) / (2 x 3)

A = 8/3

B = 1 - 7/16 - 1/2

B = (1 x 16) / (1 x 16) - 7/16 - (1 x 8) / (2 x 8)

B = 16/16 - 7/16 - 8/16

B = 1/16

13)

A = 1/2 + 5/3

A = (1 x 3) / (2 x 3) + (5 x 2) / (3 x 2)

A = 3/6 + 10/6

A = 13/6

B = 3/4 + 2/5

B = (3 x 5) / (4 x 5) + (2 x 4) / (5 x 4)

B = 15/20 + 8/20

B = 23/20

C= 3/4 + 4/5

C = (3 x 5) / (4 x 5) + (4 x 4) / (5 x 4)

C = 15/20 + 16/20

C = 31/20

D = 5/6 + 9/4

D = (5 x 2) / (6 x 2) + (9 x 3) / (4 x 3)

D = 10/12 + 27/12

D = 37/12

E = 2/9 + 5/6

E = (2 x 2) / (9 x 2) + (5 x 3) / (6 x 3)

E = 4/18 + 15/18

E = 19/18

F = - 1/14 + 1/21

F = (1 x 3) / (14 x 3) + (1 x 2) / (21 x 2)

F = 3/42 + 2/42

F = 5/42.