x-pretul initial
10% din x= 10/100 * x= 1/10 * x= x/10 -scumpirea
x+x/10 = (10x+x)/10= 11x/10 - noul pret
11x/10 = 55
x=10*55/11
x=10*5
x=50 lei
x-pretul initial
20% din x= 20/100 * x= 1/5 * = x/5 -ieftinire
x-x/5= (5x-x)/5= 4x/5 -noul pret
4x/5= 48
x=5*48/4
x=5*12
x=60