Question 402112
ST Paul Island in Alaska has 12 fur seal rookeries ( breeding place) .
in 1961, to estimate the fur seal pup population in the Gorbath rookery, 4963 fur
 seal pups were tagged in early August.
In late August, a sample of 900 pups was observed and 218 of these were found to have been previously tagged. 
Estimate the total number of fur seal pups in this rookery.
:
A ratio equation:
Let e = estimated number
:
{{{e/900}}} = {{{4963/218}}}
Cross multiply
218e = 900 * 4963
:
218e = 4466700
:
e = {{{4466700/218}}}
e = 20,489