5a+2b=36
a/4=b/5=c/12=k
=> a=4k; b=5k; c=12k
5a+2b=5·4k+2·5k
30k=36 => k=36/30=6/5 (sau 1,2)
a=4·6/5=24/5=4,8
b=5·6/5=6
c=12·6/5=72/5=14,4
R: a=4,8; b=6; c=14,4
sau a=24/5; b=6; c=72/5
verificare: 4,8 /4 = 6/5 = 14,4 /12 =1,2
5a+2b=5·4,8+2·6=24+12=36 (A)
