Question

2x-y=10 e x+2y=55, qual o valor de x+y?

Answer 1

$\left \{ {{2x-y=10} \atop {x+2y=55}} \right.$

2x-y=10
2x=10+y
x= $\frac{10+y}{2}$

x+2y=55
$\frac{10+y}{2}$ + 2y= 55
$\frac{10+y+4y=110}{2}$
10+5y=110
5y=110-10
5y= 100
y= 100/5
y= 20

x= $\frac{10+y}{2}$
x= $\frac{10+20}{2}$
x= $\frac{30}{2}$
x= 15