2. Why did the large states want voting in Congress to be based on population?

To be fair, they would count 3/5 slaves as 1 person

The issue at the time was deciding on the large and small states' population in the Congress. The big states such as Virginia wanted to have representatives and senates to count by population. Means that the more people you have in the state, the more power you have in the Congress. The small states disagrees because they have less people therefore the big states will over power them. They want each state to have the same number of representatives in the Congress. States compromised at the end with the Great Compromise.