Question

Calculati: 5x + 7y +2z stiind ca x + y = 123 si y + z = 257

Answer 1

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