x-pretul initial
10% din x= 10/100 * x= 1/10 * x= x/10 -cresterea
x+x/10= (10x+x)/10= 11x/10-noul pret
10/100 * 11x/10= 10/100 * 11x/10= 1/10 * 11x/10= 11x/100-scaderea
11x/10 -11x/100= (110x-11x)/100= 99x/100 -noul pret
99x/100 = 118 800
x=118 800*100/99
x=1200 *100
x=120000