Notam pretul produsului cu P
prima ieftinire :
P-10
a doua ieftinire;
(P-10)-(P-10)*20/100=D
(P-10)-(P-10)*1/5=D
P-10-P/5+2=D
P*5/5-P/5-8=D
P*4/5-8=D
Daca l-am scumpi
D+D*30/100=P
D+D*30/100=P
D*10/10+D*3/10=P
D*13/10=P
D=P*10/13
=>P*4/5-8=P*10/13
P*4/5-P*10/13=8
P*52/65-P*50/65=8
P*2/65=8
P*2=520
P=520:2
P=260 lei