18 a b c
I-----I------------I-----I----I
a=(18+b+c)/2
b=(18+a+c)/3
c=(18+a+b)/5
2a=18+b+c (1)
3b=18+a+c (2)
5c=18+a+b (3)
din (1) scad (2)
2a-3b=18+b+c-18-a-c
2a-3b=b-a
3a=4b
b=3a/4
din (3) scad (2)
5c-3b=18+a+b-18-a-c
5c-3b=b-c
6c=4b
3c=2b
c=2b/3=(2×3a/4)/3=a/2
inlocuim in (1) pe b si pe c in functie de a
2a=18+3a/4+a/2
8a=72+3a+2a
3a=72
a=24 m
b=3×24/4=18 m
c=24/2=12 m