Réponses

2014-05-08T15:05:11+02:00
Soit x le prix du croissant
et y le prix du pain

on sait que

4x +5y =7.25
6x + 7y = 10.45

4x = 7.25-5y
x = 7.25/4 -5/4 y

donc
6x+7y = 10.45
6 (7.25/4 -5/4y) +7y = 10.45
43.50 /4-30/4y +7y =10.45
-15/2y +7y = 10.45-43.50/4
-15/2y +14/2y = 41.80 /4 -43.50/4
-1/2 y = - 1.70/4
y = -1.70/4 x -2
y =  0.85

6x+7y = 10.45
6x +7x0.85 = 10.45
6x +5.95 = 10.45
6x = 10.45 -5.95
6x = 4.50
x =4.50 /6
x =  0.75

un croissant coute 0.75 euros et un pain 0.85