Réponses

2014-03-09T20:36:18+01:00
A = 1/7 + 2/28
a = 4/28 + 2/28 = 6/28 = 3/14

b = 21/4 : 12/5
b = 21/4 x 5/12 = 105/ 48 = 35/16
Meilleure réponse !
2014-03-09T21:18:19+01:00
A = 1/7 + 1/4 x 2/7  
A = 1/7 + 1 x 2
               4 x 7
A = 1/7 + 2/28
A = 1 x 4 / 7 x 4 + 2/28
A = 4/28 + 2/28
A = 6/28
A = 2 x 3 / 2 x 14
A = 3/14

B = 21/4 :12/5
B = 21/4 x 5/12
B = 21 x 5
      4 x 12
B = 105/48
B = 3 x 35 / 3 x 16
B = 35/16