1a chache of 100 at a distance 100 miles from base
2nd cache of 100 at a distance 200 miles from base
3rd cache of 100 at a distance 300 miles from base
the truck starts with 500, crosses first 100 miles ,so loses 100 fuel then refuells to regain full tank. similarly for the next 200 miles
so at 300 miles it will have full tank and 500 miles more to go which it crosses easily
TO PUT THE CHACHES
first travel 100 miles dump 300 fuel and return this is dump 1
then again travel 100 miles , take 100 fuel from dump 1
travel the next 100 miles , dump 200 fuel and return,this is dump 2
so dump 1=200, dump2=200
then travel 300 miles and dump 100 fuel this is dump 3
come back till dump 2 and take 100 fuel
go till dump 1 and take 100 fuel
return to base
so the refuelling stations are ready