Gasoline required to cross a desert?

i think 4 pay loads

hey nishant check this plz i am waiting for an answer

a 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

build a station at 200 miles (station 1) and 300 miles (station 2).
First 5 loads: dump 100 at first station, so now there's enough for 500 miles at station 1.
6th trip: take 500 from border, tank 100 at station 1, dump 200 at station 2 and go back to station 1; now there's 400 at station 1 and 200 at station 2.
7th trip: take the 400 from station 1, go station 2 and tank the 200, with the 500 in the truck the desert can be crossed.