Question

josias comprou 5 canetas e 3 lapis gastou R$21,10 mariana comprou 3 canetas e 2 lapis gastou 12,90 fernanda comprou 2 canetas e 5 lapis .Quanto eles gastou

Answer 1

$5x+3y=21,10\\3x+2y=12,90\\2x+5y=?$

Vamos calcular....
$2x+5y=?\\2x=5y\\x= \frac{5y}{2}$
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$3x+2y=12,90\\\\3.( \frac{5y}{2})+2y=12,90\\\\ \frac{15y}{2} +2y=12,90\\\\ \frac{15y+4y}{2}=12,90 \\\\ \frac{19y}{2} =12,90\\\\9,5y=12,90\\\\y= \frac{12,90}{9,5} =1,3578$
Então, o lápis (y) custa 1,36 (aproximadamente)
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$5x+3y=21,10\\5x+3.(1,36)=21,10\\5x+4,08=21,10\\5x=21,10-4,08\\5x=17,02\\x= \frac{17,02}{5} =3,404$
Então a caneta (x) custa aproximadamente 3,40
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Agora vamos descobrir o custo de Fernanda:
$2x+5y=?\\2.(3,40)+5.(1,36)=?\\6,80+6,80=13,60$

Então, Fernanda gastou R$ 13,60