Respostas

2013-11-25T17:00:03-02:00
Y+y=10
2y=10
y=10/2
y=5

Substituindo na segunda 

5x+20y=140
5x+20.5=140
5x=140-100
5x=40
x=40/5
x=8

S={8,5}
2013-11-25T17:00:22-02:00
Y + y = 10
5x + 20y = 140

2y  = 10
y = 10 ÷ 2
y = 5
Vamos encontrar o valor de x:
5x + 20y = 140
5x + 20 * 5 = 140
5x + 100 = 140
5x = 140 - 100
5x = 40
x = 40 
÷ 5
x = 8

Resposta: 
x = 8
y  = 5