Wprowadźmy oznaczenia:

x - cena wafelka

y- cena gałki lodów

 

$\{\begin{array}{l}2x+2\cdot 2y=5,8\\ 3x+3\cdot 3y=12,3\end{array}$    

$\{\begin{array}{l}2x+4y=5,8\mid :2\\ 3x+9y=12,3\end{array}$  

$\{\begin{array}{l}x+2y=2,9\\ 3x+9y=12,3\end{array}$  

$\{\begin{array}{l}x=2,9-2y\\ 3\cdot \left(2,9-2y\right)+9y=12,3\end{array}$  

$\{\begin{array}{l}x=2,9-2y\\ 8,7-6y+9y=12,3\end{array}$  

$\{\begin{array}{l}x=2,9-2y\\ 3y=3,6\end{array}$  

$\{\begin{array}{l}x=2,9-2y\\ y=1,2\end{array}$  

$\{\begin{array}{l}x=2,9-2\cdot 1,2\\ y=1,2\end{array}$  

$\{\begin{array}{l}x=2,9-2,4\\ y=1,2\end{array}$  

$\{\begin{array}{l}x=0,5\\ y=1,2\end{array}$  

 

Odp.: Gałka lodów kosztuje 1,20 zł, a wafelek 0,50 zł.