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Exercice 8 : (Sur le cahier) Calcule et donne le résultat sous la forme la plus simple possible.
a) 1/5 + 3/5 b) -5/9 + 1/9 c) 4/11 − 7/11 d) 7/4 − 1/4

e) 4/7 + 3/4 + 2/7 + 5/4 + 1/7 f) 7/5 + 4/20 g) 4/9 − 2/3

h) 5/6 − 7/18 i) 7/6 + 9/8 j) − 7/12 + 7/9


Répondre :

a) 1/5 + 3/5 = (1+3)/5 = 4/5

b) -5/9 + 1/9 = (-5+1)/9 = -4/9

c) 4/11 - 7/11 = (4-7)/11 = -3/11

d) 7/4 - 1/4 = (7-1)/4 = 6/4 = 3/2

e) 4/7 + 3/4 + 2/7 + 5/4 + 1/7 = (16/28) + (21/28) + (8/28) + (35/28) + (4/28) = 84/28 = 3

f) 7/5 + 4/20 = (28/20) + (1/5) = 7/5 + 4/20 = 7/5 + 1/5 = 8/5

g) 4/9 - 2/3 = (4/9) - (6/9) = -2/9

h) 5/6 - 7/18 = (15/18) - (7/18) = 8/18 = 4/9

i) 7/6 + 9/8 = (28/24) + (27/24) = 55/24

j) -7/12 + 7/9 = (-7/12) + (28/36) = -7/12 + 7/12 = 0