Question

i usually catch the bus home from work.i get on at the first stop and have about 10 km to travel ,so i usually nod off to sleep.i normally fall asleep when the bus has about 3 times as far to go as it has already travelled.halfway through the trip i tend to wake up and then i finally fall to sleep again when the bus has 3 quarters of the remaining distance to go.i wake up just in time to get off at the right bus stop.what portion of the trip do i usually sleep?