Bonjour , Ma soeur ( 4éme) a besoin d'aide SVP: EXERCICE 2: Dénominateur différents ( 5 PTS ): a/ 3÷4 + 4÷5 = .................... b/ -2÷9 + 3÷5 = ............

Bonjour,

a) 3/4 + 4/5

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

= 15/20 + 16/20

= 31/20

b) - 2/9 + 3/5

= (- 2 x 5) / (9 x 5) + (3 x 9) / (5 x 9)

= - 10/45 + 27/45

= 17/45

c) 1/7 + - 3/8

= 1/7 - 3/8

= (1 x 8) / (7 x 8) - (3 x 7) / (8 x 7)

= 8/56 - 21/56

= - 13/56

d) - 1/7 + 4/5

= (- 1 x 5) / (7 x 5) + (4 x 7) / (5 x 7)

= - 5/35 + 28/35

= 23/35

e) - 1/9 + 3/10

= - (1 x 10) / (9 x 10) + (3 x 9) / (10 x 9)

= - 10/90 + 27/90

= 17/90.