A student estimated the number of minnows (a small fish) in a section of a stream. She caught and marked 150 minnows and released them. The next day she caught 120 minnows, of which 45 were marked.
Calculate the estimated number of minnows in this section of the stream. Show your working.
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The marks made the minnows slightly easier for predators such as herons to see and catch. Explain how this would affect the estimated population size.
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