Please help me with this proportion problem

Question

An environmental scientist wants to estimate the number of carp in a pond. He captures a 100 carp and tags them all. Then he releases them. A week later he captures 85 carp and records how many have tags. 20 of them were tagged and 65 were not tagged. Write and solve a proportion to estimate the number of carp in the pond.

Answer 1

20/85 = 23.53% of carp have tags.

65/85 = 76.47% of carp have no tags.

 

We know that 100 carp have tags, and that 23.53% carp have tags, so 100 carp must be 23.53% of all carp in the pond. The proportion then looks like this:

 

100 carp = 23.53%

X carp = 100%

 

X = (100 * 100%)/23.53% = 425

 

So, there are 425 carp in the pond.