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Exercice 15

A = 20/4 +3/4 = 23/4  

B=2/3  +12/3 = 14/3   

D = 9/2 -6/2 =  3/2 

E = 4 - 5/6 = 24/6 - 5/6 = 19/6

Exercice 15 :
A = 5 + 3/4
   = 5/1 + 3/4
   = 20/4 + 3/4
   = 23/4

B = 2/3 + 4
   = 2/3 + 4/1
   = 2/3 + 12/3
   = 14/3

D = 9/2 - 3
   = 9/2 - 3/1
   = 9/2 - 6/2
   = 3/2

E = 4 - 5/6
   = 4/1 - 5/6
   = 24/6 - 5/6
   = 19/6

Exercice 16 :
G = 3 + 3/4
   = 3/1 + 3/4
   = 12/4 + 3/4
   = 15/4

H = 7/3 + 2
   = 7/3 + 2/1
   = 7/3 + 6/3
   = 13/3

J = 4 - 2/3
  = 4/1 - 2/3
  = 12/3 - 2/3
  = 10/3

K = 7/3 - 2
   = 7/3 - 2/1
   = 7/3 - 6/3
   = 1/3