abc:5=bc rest a
=>abc+a= nr.abc
=>(abc+a):5=((bc+a)*5)+a
=>(4a*5):5=a
a=(4*5):5
a=20:5
a=4
=>(4bc+4):5=((bc+4)*5)+4
=>(2*5):2=c
c=10:2
c=5
=>(4b5+4):5)=((b5+4)*5)+4
=>b=a+c
=>b=4+5
b=9
=>(495+4):5=((95+4)*5)+4
=>499:5=99*5+4
=>499:5=495+4
=>499=499
numarul abc=499
abc:5=bc rest a
499:5=99 rest 4
abc=495+4
abc=499