Biologists tagged 69 fish in a lake on January 1 On February

Biologists tagged 69 fish in a lake on January 1. On February 1, they returned and collected a random sample of 22 fish, 11 of which had been previously tagged. On the basis of this experiment, approximately how many fish does the lake have?

Solution

Given that biologist tagged 69 fish in a lake on January.

On February 1, they collected a random sample of 22 fish, 11 of which had been previously tagged.

Need to find the number of fish that the lake have.

Out of 22 fish, 11 are previously tagged in means the number of fish is double of the fish tagged in (i.e., 22 = 2*11)

For 69 tagged fish there will be 2*69 = 138 fish.

Therefore, the number of fish in the lake approximately is 138fish.