Samuel slept for 1/4 of the distance.
From the information, Samuel fell asleep halfway home.
He didn't wake up until he still had half as far to go as he had already
gone while asleep. Consider that the total distance covered was 1.
Then from the first point we know that Samuel fell asleep after covering a distance of 1/2.
It is provided that he woke up only after covering half of the remaining distance. This will be:
= 1/2 * 1/2
= 1/4
That is, he slept for 1/4 of the remaining distance. Thus, Samuel was asleep for 1/4th of the entire trip home.