Réponses

2014-05-26T15:45:40+02:00
Emma : x croissants
Fred :  x+3 croissants
Lou : 2x croissants
On a donc :
x+x+3+2x = 39
4x +3 = 39
4x = 39-3
4x = 36
x = 36/4
x = 9
Emma a acheté 9 croissants
Fred : 9+3 = 12
Lou : 2x9 = 18
Vérification :
9+12+18 = 39 
2014-05-26T15:49:28+02:00
Emma x
fred x+3
louis 2x
donc x+x+3+2x=39
4x+3=39
4x=39-3
4x=36
x=36/4=9

emma =>9
fred =>9+3=12
louis=>9*2=18

9+12+18=39