Bonjour, « Calculer en réduisant d’abord au même dénominateur » Merci d’avance.

Bonjour,

4/5 + 9/15

= (4 x 3) / (5 x 3) + 9/15

= 12/15 + 9/15

= 21/15

= (3 x 7) / (3 x 5)

= 7/5

- 2/3 + 29/18

= (- 2 x 6) / (3 x 6) + 29/18

= - 12/18 + 29/18

= 17/18

- 4/9 - 35/63

= - 4/9 (- 7 x 5) / (7 x 9)

= - 4/9 - 5/9

= - 9/9

= - 1

- 3/8 + 12/40

= (- 3 x 5) / (8 x 5) + 12/140

= - 15/40 + 12/40

= - 3/40

25/36 - 9/6

= 25/36 - (9 x 6) / (6 x 6)

= 25/36 - 54/36

= - 29/36

17/90 - 3/12

(17 x 2) / (90 x 2) - (3 x 15) / (12 x 15)

= 34/180 - 45/180

= - 11/180

- 6/11 - 11/33

= (- 6 x 3) / (11 x 3) - 11/33

= - 18/33 - 11/33

= - 29/33

4/7 - 12/14 + 19/28

= (4 x 4) / (7 x 4) - (12 x 2) / (14 x 2) + 19/28

= 16/28 - 24/28 + 19/28

= 11/28.

3/4 - 9/20 + 24/20 + 3/5 - 12/20

= (3 x 5) / (4 x 5) - 9/20 + 24/20 + (3 x 4) / (5 x 4) - 12/20

= 15/20 - 9/20 + 24/20 + 12/20 - 12/20

= 30/20

= (10 x 3) / (10 x 2)

= 3/2.