1)12:1/6 =8: 1/x
12*6/1 =8*x/1
12*6 =8x
x =72/8
x =9 zile
2)z*(100-30) /100 =210
x *70 /100 =210
x =210*100 /70 =300
3)320*(100-30 ) /100=320*70/100 =224 (reducerea cu 30%)
224*(100+40) /100 =224*140 /100 =313 (majorarea cu 40% )
4)x *(100+20) /100 =420
x =420*100/120
x =350 (pretul initial )