Odpowiedź:
x - pieniądze siostry
y - pieniądze brata
[tex]\left \{ {{x+y=495} \atop {0,9x=1,2(0,1x+y)}} \right. \\ \left \{ {{x+y=495} \atop {0,9x=0,12x+1,2y}} \right.\\ \left \{ {{x+y=495} \atop {0,78x-1,2y=0}} \right.\\ \left \{ {{x+y=495} \atop {\frac{78}{120}x-1y=0 }} \right. \\ \frac{198}{120}x=495\\\\ x=300\\ y=495-300\\ \left \{ {{x=300} \atop {y=195}} \right.[/tex]
