Answer:
When Northern and Southern delegates met in the Constitutional Convention, the huge question of slavery had to be addressed. The South wanted to count their enslaved population as part of them during censuses but the North objected to this saying that if the Blacks were not allowed to vote, they should not be counted.
A compromise was reached which was called the Three-fifths clause. This clause stated that every enslaved person would be counted as three-fifths of a person which meant that for every 5 enslaved people, 3 would be counted as humans. This therefore increased the population and by extension, the political power of the South.
The attitude shown here by delegates towards African-Americans was one of superiority. They did not think of African-Americans as people but rather as sub-humans that did not amount to a single human.