pf = pret final
pi = pret initial
pf = pi + pr% din pi
pf1 = 10/10 + 1/10 = 11/10
pf2 = 11/10 - 1/10 * 11/10 = 11/10 - 11/100 = (110 - 11)/100 = 99/100
pf2 = 99/100
1980/1 = 99/100 = 198000/99 = 2000
pi = 2000
verificare: 2000 + 10% = 2000 + 200 = 2200
2200 - 10% = 2200 - 220 = 1980
Multa bafta