daca x = lungimea drumului intreg , atunci
aduc la numitor comun fractiile 1/3 ; 2/5 si obtin [3;5]=15 ⇒ 5/15 si 6/15
prima zi se parcurge ... 5x / 15 raman ... 15x / 15 - 5x / 15 = 10x / 15 *
a doua zi ,, ,, ... 6x / 15 * 10x / 15 = 60x / 225 = 4x / 15 **
raman ... 10x / 15 - 4x / 15 = 6x / 15 care ,
a 3 -a zi ,, ,, ... 6x / 15 = 2,4km ***
↓
x = 2,4 *15 : 6 = 6km