Question

Clive wants to estimate the number of fish in apond.

Clive catches 50 fish from the pond. He marks each fish with a dye.
He then puts the fish back in the pond.
The next day, Clive catches 40 fish from the pond. 8 of these fish have been marked with the dye.
Work out an estimate for the number of fish in the pond.

Answer 1

Answer: 50

Explanation
One method to estimate the number of fish in the pond is to use the mark-and-recapture method. This method assumes that the proportion of marked fish in the second sample is the same as the proportion of marked fish in the entire population. Using this assumption, we can estimate the total number of fish in the pond as follows:

Let N be the total number of fish in the pond.

Let M be the number of fish caught in the first sample (50 fish).

Let R be the number of marked fish caught in the second sample (8 fish).

Let r be the unknown total number of marked fish in the pond.

According to the mark-and-recapture method, we have the following proportion:

M/N = R/r

We can rearrange this equation to solve for N:

N = M * r / R

Substituting the values given in the problem, we have:

N = 50 * r / 8

Simplifying, we get:

N = 6.25 * r

This means that the estimated total number of fish in the pond is 6.25 times the number of marked fish in the second sample. Since we know that 8 fish were marked in the second sample, the estimate for the total number of fish in the pond is:

N = 6.25 * 8 = 50

Therefore, the estimated number of fish in the pond is 50