Question

540 soles se componen de 78 billetes de 10 y 5 soles. Calcular el número de billetes de 5 soles

Answer 1

Billetes de 10: x
Billetes de 5: y

$\left \{ {{x+y=78} \atop {10x+5y=540}} \right. \\ \\ x=78-y \\ 10(78-y)+5y=540 \\ 780-10y+5y=540 \\ 780-540=5y \ \\ \ y= \frac{240}{5} \\ y=48 \\ x=78-y \\ x=30$