Question

TENHO QUE COMPRAR LAPIS E CANETAS SE COMPRAR LAPIS E TRES CANETAS GATEREI 16,50 SE COMPRAR 5 LAPIS E QUATRO CANETAS GATEAREI 15,50 QUAL O PREÇO DE CADA LAPIS E CANETA

Answer 1

Seja c = caneta   e   l = lápis

$\begin{cases}7l+3c=16,5\\ 5l+4c=15,5\end{cases}\\\\\\\\ 7l+3c=16,5\to~~ 3c=-7l+16,5\to~~c= \dfrac{-7l+16,5}{3} \\\\\\\\5l+4c=15,5\to~~5l+4\left( \dfrac{-7l+16,5}{3} \right)=15,5\to\\\\ 5l+\left( \dfrac{-28l+66}{3} \right)=15,5\to~~ mmc=3\to~~15l-28l+66=46,5\to\\\\ -13l=46,5-66\to~~-13l=-19,5~(-1)\to~~ 13l=19,5\to\\\\ l= \dfrac{19,5}{13}\to~~ \boxed{l=1,5}$



$c= \dfrac{-7l+16,5}{3}\to~~c= \dfrac{-7*1,5+16,5}{3}\to~~ c= \dfrac{-10,5+16,5}{3}\to\\\\ c= \dfrac{6}{3}\to~~\boxed{c=2}\\\\\\\\ \large\boxed{\boxed{S=\{1,5~;~2\}}}$



Resposta: Cada lápis custa R$ 1,50 e cada caneta custa R$ 2,00.