Question

Suma a două numere este 225 , iar diferența lor este 15.
Să se afle cele două numere .

Answer 1

a+b=225
a-b=15, a=15+b

15+b+b=225
2b=225-15
2b=210, b=105, a=120

Answer 2

$\left \{ {{x+y=225} \atop{x-y=15}} \right \Longleftrightarrow \left \{ {{x=225-y} \atop {225-y-y=15}} \right. \Longleftrightarrow \left \{ {{x=225-y} \atop {225-2y=15}} \right. \Longleftrightarrow \\ \Longleftrightarrow \left \{ {{x=225-y} \atop {2y=225-15}} \right. \Longleftrightarrow \left \{ {{x=225-y} \atop {2y=210}} \right. \Longleftrightarrow \left \{ {{x=225-y} \atop {y= \frac{210}{2} }} \right. \Longleftrightarrow$
$\Longleftrightarrow \left \{ {{x=225-y} \atop {y=105}} \right. \Longleftrightarrow \left \{ {{x=225-105} \atop {y=105}} \right. \Longleftrightarrow \left \{ {{x=120} \atop {y=105}} \right. ;$