|-------------|-------------|------------| a
1/3
|------|-----|------|------| b = traseul ramas = 2/3din a
1/4 +12 km =b
12 km reprezinta 3/4 din b => b= 12:3x4 = 16 km
16 km reprezinta 2/3 din a => a= 16:2x3 =24 km a parcurs alpinistul
verificare: 24:3 =8 km in prima etapa
24-8=16 km traseul ramas
16:4=4 km in etapa II
16-4 =12km in etapa III