Trout are a type of fish that live in freshwater ponds and streams. Raychelle did an investigation to see how the amount of nitrogen in pond water affects the number of trout in the water. She tested the water of 20 different ponds in her city. Each one had a different amount of nitrogen in it. She then did a study to determine the number of trout in each pond. She compared the amount of nitrogen to the number of trout in each pond. What was Raychelle's dependent variable?

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