Răspuns :
Fie numerele a si b
a+b=390
a÷b=4=>
a=b×4.inlocuim in a+b=390
b×4+b=390=>5b=390=>b=78=>a=312
a+b=390
a÷b=4=>
a=b×4.inlocuim in a+b=390
b×4+b=390=>5b=390=>b=78=>a=312
[tex]x + y = 390 \\ x \div y = 4 \\ x = 4y \\ 4y + y = 390 \\ 5y = 390 \\ y = 390 \div 5 \\ y = 78 \\ x = 4y \\ x = 4 \times 78 \\ x = 312[/tex]