a/2=b/3=c/4
Spunem ca fractiile sunt egale cu x
a/2=b/3=c/4=x
a=2x, b=3x, c=4x
a'/17=b'/13=c'/15=y
a'=17y, b'=13y, c'=15y
a'=a+5600
17y=2x+5600
Dar a+b+c=a'+b'+c'
a+b+c=a+5600+b'+c'
b+c=b'+c'+5600
3x+4x=13y+15y+5600
7x=28y+5600
7x=7(4y+800)
x=4y+800
Inlocuim
17y=2x+5600
17y=2(4y+800)+5600
17y=8y+1600+5600
9y=7200
y=800
a'=17*800=13600
b'=13*800=10400
c'=15*800=12000
a=a'-5600=8000
2x=8000
x=4000
b=12000
c=16000