7/20 din x= 7/20 *x = 7x/20 - prima data
x-7x/20= (20x-7x)/20= 13x/20 -restul
1/5 din 13x/20= 1/5 * 13x/20= 13x/100 -a doua oara
13x/20 -13x/100= (65x-13x)/100= 52x/100 -noul rest
52x/100=624
x=100*624/52
x=100*12
x=1200
13*1200/100= 13*12= 156 a parcurs a doua oara