3a=4b=5c=k (k-coeficient de proportionalitate)
=>a=k/3
=>b=k/4
=>c=k/5
Stim suma numerelor =>k/3 + k/4 + k/5 = 47/10
Numitorul comun este 60
20k+15k+12k=282
47k=282 =>k=6
=>a=6/3=2
=>b=6/4=3/2
=>c=6/5
Verificare : 2 + 3/2 + 6/5 =
Numitor comun 10
(20+15+12)/10 = 47/10 = 4,7