Question

raluca are 200 lei in bancnote de 10 si 5 lei 

daca are in total are 28 de bancnote aflati cate bancnote de 5 lei are  raluca

 

Answer 1

10*x+5*y=200

10x+5y=200
x+y=28/-10

10x+5y=200
-10x-10y=-280
================(+)
-5y=-80
y=80:5
y=16 bancnote de 5 lei

x+16=28
x=28-16
x=12 bancnote de 10 lei

Answer 2

x=bacnote de 5 lei

y=banknote de 10 lei

{x+y=28 / x (-10)

{5x+10y=200

{-10x-10y=-280

{5x+10y=200

-5x=-80 / x (-1)

x=-80:5 =>x=16

16+y=28

y=28-16

y=12