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To estimate the population size of crabs in a certain lagoon, traps were laid at random. 400 crabs were caught, marked and released back into the
lagoon. Four days later, traps were laid again and crabs were caught. Out of the 374 crabs, 80 were found to be marked.
(a) Calculate the population size of crabs in the lagoon using the formula below.
N=#frac{ntimesM}{m}#
N=Total population of crabs in the lagoon.
n=Total number of crabs in the second catch.
M=Number of marked crabs during the first catch.
m=Number of marked crabs in the second catch.
(b) State two assumptions that were made during the investigation.
(c) What is the name given to this method of estimating the population size?