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7/9 + 11 /15 =  35/45 + 33/45 =  68/45

7/8 + 22 /12 =  7/8 + 11/6  = 21/24 + 44/24 = 65/24

6/5 + 3 /8 =  48/40 + 15/40 = 63/40

15/18 - 5 /27  = 5 /6 - 5 /27 = 45/54 - 10/54 = - 35/54

ranouche05

Réponse:

a) 7/9 + 11/15 = 7x15/9x15 + 11x9/15x9

= 105/135 + 99/135

= 105+99/135

= 204/135

= 68/45

b) 7/8 + 22/12 = 7x3/8x3 + 22x2/12x2

= 21/24 + 44/24

= 21+44/24

= 65/24

c) 6/5 + 3/8 = 6x8/5x8 + 3x5/8x5

= 48/40 + 15/40

= 48+15/40

= 63/40

d) 15/18 - 5/27 = 15x3/18x3 - 5x2/27x2

= 45/54 - 10/54

= 45-10/54

= 35/54