The full text can be found in Article 1, Section 2 of the U.S. Constitution: "Representatives and direct Taxes shall be apportioned among the several States which may be included within this Union, according to their respective Numbers, which shall be determined by adding to the whole Number of free Persons, including those bound to Service for a Term of Years, and excluding Indians not taxed, three fifths of all other Persons (emphasis mine.)" To sum up: taxes and representation will be population based (just like today) but we won't count Indians on reservations and slaves will only count as 3/5 a person when conducting a census. See, originally the federal government was to receive taxes based on land values. But, just as any homeowner knows, the lower the value of one's home/land, the lower their tax burden. The states practiced this frequently which became a problem for the fledgling Washington government when trying to raise revenue.
This next part is simple. During the Constitutional Convention in the late 1700's, the South was for slavery and the North was against it. The Northern states wanted to ban it all together but the Southern states really enjoyed the free labor that gathered cotton and boosted their economic output. So, when deciding how to count the population, the South wanted each slave to count as 1 person, while the North wanted them to not count at all. "*GASP* The North was full of racists and bigots!" some will say. Not true. The blatant hypocrisy of the Southern states is almost laughable. It's not that the South wanted to afford slaves the right to vote, in fact, it was quite the opposite. They simply wanted them counted among the population in order to increase their representation in Congress. This would give the South more votes than the North, thereby making it impossible for the North to abolish slavery. The "Three-Fifths Compromise" was actually a product from the Northern states. It was a way to decrease the South's population count in Congress while still getting the South to sign on to the U.S. Constitution. Without this compromise, the Constitution would have never been ratified and we'd have a much different country than we do today.
So why did the Republicans in Congress skip over this section (they also skipped over the 18th Amendment which abolished Liquor, but that's a little off topic)? As I stated above, it was either ignorance or cowardice. When editing papers in high school or college, people correct and erase their mistakes before turning in a finished paper. But the Constitution is a very unique document as it contains all Amendments, even those repealed by amendments made in the future (mistakes). This is so we learn what was done, why it was done, and why it's no longer in practice today. Since the Republicans skipped this section in reading the Constitution, they also skipped the opportunity to have a national discussion about what the clause actually meant. And that in itself was a mistake.
