Bonjour

1)

85/15 = (5 x 14) / (5 x 3) = 14/3

11/12 = irréductible

12/15 = (3 x 4) / (3 x 5) = 4/5

49/59 = (7 x 7) / (7 x 8) = 7/8

54/81 = (27 x 2) / (27 x 3) = 2/3

303/273 = (3 x 101) / (3 x 91) = 101/91.

2)

8/16 = (8 x 1) / (8 x 2) = 1/2 donc oui 8/16 = 1/2

15/25 = (5 x 3) / (5 x 5) = 3/5 et 5/10 = (5 x 1) / (5 x 2) = 1/2

donc non car 3/5 ≠ 1/2

28/36 = (4 x 7) / (4 x 9) = 7/9 donc oui 28/36 = 7/9

42/56 = (14 x 3) / (14 x 4) = 3/4 = (3 x 2) / (4 x 2) = 6/8 donc oui 42/56 = 6/8.

3)

1/3 = (1 x 5) / (3 x 5) = 5/15

2/5 = (2 x 3) / (5 x 3) = 6/15

5/6 = (5 x 4) / (6 x 4) = 20/24

7/8 = (7 x 3) / (8 x 3) = 21/24

3/5 = (3 x 6) / (5 x 6) = 18/30

8/6 = (8 x 5) / (6 x 5) = 40/30

1/4

3/2 = (3 x 2) / (2 x 2) = 6/4

9/12

4/2 = (4 x 6) / (2 x 6) = 24/12

4/36

4/9 = (4 x 4) / (4 x 9) = 16/36.