1)a+b+c=650
a=b-25,c:b=4 rest 15,c=4b+15
b-25+b+4b+15=650
6b=660
b=110
a=110-25=85
c=440+15=455
85+110+455=650
2)a+b+c=450
a=b+15
c:b=3 rest 15⇒c=3b+15
b+15+b+3b+15=450
5b=450-30
5b=420
b=420:5
b=84
a=84+15
a=99
c=3x84+15
c=267
Verificare : 99+84+267=450
3)x-peimul frate
y-al doilea frate
z-al treilea frate
x+y+z=786
y=13+x.1/2 ⇒x=2y-26
y=z.1/4⇒z=4y
inlocuind in prima⇒
2y-26+y+4y=786
7y=786+26=812
y=812:7=116
x=2y-26=116.2-26=206
z=4y=116.4=464
