Question

a biologist originally marked 40 butterflies in Wilson Park. Over a month-long period butterfly traps caught 200 butterflies. of those 200, 80 were found to have tags. Based on this information, what is the estimated population size of the butterflies in Wilson Park?

Answer 1

Given merely 40 butterflies were marked, assumed that there were multiple captures of both marked and unmarked butterflies, that the butterflies caught in traps were on the loose to be caught again. There are two mathematical solutions for this, both yielding the same answer which is 100. 

• First, to each marked butterfly was taken twice (40 marked X2 = 80 captured) then of the unmarked butterflies the 120 captured must relate to 60 actual butterflies. In which 40 + 60 = 100. 

• Secondly, by means of ratios in which 80/200 = 40/X. In this case X also = 100 that will result to the estimated size of the population of wilson park is 100.