x+y = 8
(3,12*x + 2,4*y)/(x+y) = 2,85
(312/100*x + 240/100*y) / 8 = 285/100
312/100*x + 240/100*y = 285*8/100
312x + 240y = 2280
Dar x+y = 8, adica y = 8-x
Inlocuim si obtinem:
312x + 240(8-x) = 2280
312x+ 1920 - 240x = 2280
72x = 2280-1920
72x = 360
x = 360/72
x = 5
y = 8-x = 8-5
y = 3