5x+7y+2z=n
x+y=123
x+z=257
x+z=?
n=?
(x+z)-(x+y)=2y
2y=257-123
2y=134
y=134:2
y=67
x+y=123
x=123-y
x=123-67
x=56
z+y=257
z=257-y
z=257-67
z=190
x+y=56+67=123
y+z=67+190=257
x+z=56+190=246
x+y+z=56+67+190=313
5x+7y+2z=n
n=(5*56)+(7*67)+(2*190)
n=280+469+380
n=1129
5x=280
7y=469
2z=380
numarul este 1129
Verificare
(280:5)+(469:7)+(380:2)=x+y+z
56 + 67 + 190 = 313
deci=> x=56.......5x=280
y=67........7y=469
z=190......2z=380
