5. fie x pretul initial
x-10/100×x=40.5
x(1-10/100)=40.5
x(100/100-10/100)=40.5
x×90/100=40.5
x=40.5 × 100/90
x=40.5×10/9
x=405/9
x=45
deci raspunsul e d
6. x/y=3/5 deci x=3y/5
x+y=40
inlocuim
3y/5+y=40
3y/5+5y/5=40
8y/5=40
8y=200
y=25
deci x=40-25=15
3x+y=3×15+25
=45+25
=70
deci raspunsul e c
