Question 631173
We need to know how many fish are in a particular lagoon. We capture 72 fish, mark them, and then throw them back into the lagoon. The next day, 50 fish are captured and 13 were tagged from the day before. These fish are then thrown back into the lagoon. Estimate how many fish are in the lagoon. 
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# of fish/# caught and tagged  = captured of those tagged/tagged of those caught
# of fish /72 = 50/13
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# of fish = 72(50/13) = 277
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Cheers,
Stan H.