A population ecologist is studying the demographics of American bison living on a grassland in North Dakota. She captures, marks, and releases 100 bison. Later, she recaptures 100 bison and discovers that 50 were previously marked and half of those marked are of reproductive age. What is the population ecologist's estimate of how many bison in the total population are of reproductive age?
A population ecologist wants to estimate the size of a robin population. In an apple orchard, she captures 10 robins, marks them, and then releases them. She returns several weeks later and captures another 10 robins, of which 2 are robins she previously marked. The estimated population size of robins is ____.