From Newsgroup: rec.puzzles

Taken from "One Hundred Problems in Elementary Mathematics" by Hugo
Steinhaus.

ISBN 0-486-23875-X

54. How many fish are in the pond?

An ichthyologist wanted to estimate the number of fish in a pond which are suitable to be caught. He threw into the pond a net with regulation size
mesh, and after having taken the net out he found 30 fish in the net; he marked each of them with a suitable colour, and threw them all back into
the pond. The next day he threw the same net and captured 40 fish, of
which 2 had been marked. In what way did he compute (approximately) the
number of fish in the pond?
--
David Entwistle
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From Newsgroup: rec.puzzles

On 04/11/2025 08:58, David Entwistle wrote:

Taken from "One Hundred Problems in Elementary Mathematics" by Hugo Steinhaus.

ISBN 0-486-23875-X

54. How many fish are in the pond?

An ichthyologist wanted to estimate the number of fish in a pond which are suitable to be caught. He threw into the pond a net with regulation size mesh, and after having taken the net out he found 30 fish in the net; he marked each of them with a suitable colour, and threw them all back into
the pond. The next day he threw the same net and captured 40 fish, of
which 2 had been marked. In what way did he compute (approximately) the number of fish in the pond?

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There are X fish in the pond.

30 are marked S. (X-30) are not. So the proportion of marked fish
is 30/(X-30).

Give it a stir, and catch 40 completely at random, of which 2 (1
in 20) are marked.

30/(X-30) = 1/20

30 = (X-30)/20

30*20 = X-30

X = 630

less the 40 the ichthyologist has removed from the pond and not
returned, so 590.
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within
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From Newsgroup: rec.puzzles

In article <10ecjf7$3i5c6$1@dont-email.me>,
Richard Heathfield <rjh@cpax.org.uk> wrote:

...........How many fish are in the pond? How can I possibly tell? >...........How many fish are in the pond? How can I possibly tell >...........How many fish are in the pond? How can I possibly tel >...........How many fish are in the pond? How can I possibly te >...........How many fish are in the pond? How can I possibly t
...........How many fish are in the pond? How can I possibly
...........How many fish are in the pond? How can I possibly
...........How many fish are in the pond? How can I possibl
...........How many fish are in the pond? How can I possib
...........How many fish are in the pond? How can I possi
...........How many fish are in the pond? How can I poss
...........How many fish are in the pond? How can I pos
...........How many fish are in the pond? How can I po
...........How many fish are in the pond? How can I p
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.

There are X fish in the pond.

30 are marked S. (X-30) are not. So the proportion of marked fish
is 30/(X-30).

30/X

-- Richard
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: rec.puzzles

On 04/11/2025 12:19, Richard Tobin wrote:

<snip>

30/X

I think I'd better take up botany.
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: rec.puzzles


David Entwistle <qnivq.ragjvfgyr@ogvagrearg.pbz> posted:

Taken from "One Hundred Problems in Elementary Mathematics" by Hugo Steinhaus.

ISBN 0-486-23875-X

54. How many fish are in the pond?

An ichthyologist wanted to estimate the number of fish in a pond which are suitable to be caught. He threw into the pond a net with regulation size mesh, and after having taken the net out he found 30 fish in the net; he marked each of them with a suitable colour, and threw them all back into
the pond. The next day he threw the same net and captured 40 fish, of
which 2 had been marked. In what way did he compute (approximately) the number of fish in the pond?

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--
-


Total / 30 = 40 / 2

This simple method only works for Water molecules in the Ocean?
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