in prima zi parcurge 20% din drum = 20/100 D = 1/5 D ==>
au mai ramas D-D/5 = D*4/5
a doua zi = 30/100 din rest = 30/100 x 4D/5 = 12D/50
deci 1/5 D + 12D / 50 + 560 = D ==> D- 1/5D - 12D/50 = 560
50 D - 10D - 12 D = 560x 50 28D = 28000 == D = 1000 km