Question

Suppose researchers marked 800 turtles and later were able to trap a total of 300 individuals in that population, of which 150 were marked. what is the estimate for total population size

Answer 1

The estimate for the total population size is 1600.

Setting up a proportion for this, we know that 150 out of our 300 turtle sample is marked; this is the first ratio for the proportion.  We also know that we marked 800 of our total population, which we will call x:

150/300 = 800/x

Cross multiply:
150*x = 300*800
150x = 240000

Divide both sides by 150:
150x/150 = 240000/150
x = 1600