What is the three fifths compromise

The Three-Fifths Compromise dealt with how slaves would be accounted for when determining states' representation in Congress.  It was a compromise adopted during the United States Constitutional Convention in 1787.

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The Three-Fifths Compromise was a way of accounting (somewhat) for the population of slaves in states that permitted slavery.  For taxation and representation purposes, the question was whether slaves should count in the population figures.  (They were not considered voting citizens at that time.)   The Three-Fifths Compromise said that three out of every five slaves could be counted when determining a state's population size for determining how many seats that state would receive in the House of Representatives.

whose power in the senate is equal to the power of the speaker of the house?

the us constitution is a living document, meaning that it can be changed over time as the country changes.