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I need to know how many sources I should use for my assignment.
If your instructor does not provide source number guidelines in the instructions for an assignment, you can ask them how many sources they expect you to use.
A rough guideline you can also use is that you should have about as many sources as there are pages in your paper. For example, for a six page paper you should expect to use about six sources. Fewer than that, and you may not have enough to write about; more than that, and your paper may just be a summary of the sources, with no room for your own ideas.