23)
x-elevi
y-banci
x-5=2y
3(y-5)=x
3y-15-5=2y
y=20
x=40+5=45
x=20
y=45
25)
x+y+z=1575
x=2(y+z)
z=y+15
atunci
x=2(y+y+15)=4y+30
inlocuind in prima ecuatie
4y+30+y+y+15=1575
6y=1530
y=255
z=270
x=2.525=1050
26
m+f=45+2.12=69
m=2f
2f+f=29
f=23
m=46
in 1988 avem
m=46-12=34 ani
f=23-12=11 ani
27
a+b+c=100
3a=b+c
c-b=b/2⇒ c=3b/2
3a=b+3b/2=5b/2
a=5b/6
5b/6+b+3b/2=100
5b+6b+9b=600
20b=600
b=30
a=25
c=45
