How did decisions made about slavery affect the congressional representation

 I think you're talking about the three-fifths compromise? The number of delegates to congress permitted to each state are relative to population. Those who opposed slavery, did not want slaves to be counted for representation. Those who were for slavery, *did* want slaves to be counted (they get more representation in the Congress that way. The three-fifths compromise stated that each slave would count for three-fifths of one person.