In the morning, Pedro sold 35 1/2 / 2 = 17 3/4 pounds of apples.
After the morning, Pedro had 35 1/2 - 17 3/4 = 17 3/4 pounds of apples remaining.
In the afternoon, Pedro sold 17 3/4 * 8/9 = 15 4/9 pounds of apples.
After the afternoon, Pedro had 17 3/4 - 15 4/9 = 2 5/9 pounds of apples remaining.
In the evening, Pedro sold 3/4 * 2 5/9 = 1 7/9 pounds of apples.
After the evening, Pedro had 2 5/9 - 1 7/9 = 4/9 pounds of apples remaining.
Pedro did not sell 4/9 pounds of apples.
The fraction of total apples not sold is 4/9 / 35 1/2 = 4/378