(5000+100*a+10*b+0)-(300+10*a+b) +(10*a+b)=4900
(5000+100*a+10*b)-300-10*a-b+10*a+b=4900
-10*a si 10*a se reduc,la fel si -b cu b
5000+100*a+10*b-300=4900
100*a+10*b=200 //Impartim la 10
10*a+b=20 ,de unde rezulta ca ab=20
Verificare: 5200-320+20=4900
In caz ca nu stii,m-am folosit de formula abc(in baza 10) =100*a+10*b+c
