3a/2b=5/4=> 3a×4=2b×5=> 12a=10b=> a=10b/12 (care se simplifica cu 2)=>a=5b/6
3b/5c=6/7=> 5c×6=3b×7=> 30c=21b=> c=21b/30 (care se simplifica cu3)=> c=7b/10
a+b+c=1672
5b/6+b+7b/10=1672 (aduc la acelasi numitor)
5×5b/30+30b/30+7b×3/30=1672
25b/30+30b/+21b/30=1672
76b/30=1672
b=30×1672/76
b=50160/76
b=660
c=7b/10=> c=7×660/10=> c=7×66=> c=462
a= 5b/6=> a=5×660/6=> a=5×110=> a=550
