A = 13/25 - 2/5
A= 13/25 - 10/25
A = 3/25
B= -31/18 - 4/3
B= -31/18 - 24/18
B= -55/18
C= 1 - 5/42
C= 42/42 - 5/42
C = 37/42
Exercice 23 :
A = 5/2 + 3/4 + -7/8
A = 20/8 + 6/8 + -7/8
A = 19/8
B= 4/15 + 2/5 - 7/30
B= 8/30 + 12/30 - 7/30
B = 13/30
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