We are using Chi Squares to understand if descrepancies in aniaml populations are random or significant. On the developed land, 20 traps were set. 7 Road runners were caught, and two were marked. On the Undeveloepd land, 20 traps were also set, but 11 Road Runners were caught and 1 was marked. I know the formula for the chi square, x^2=sigma (observed-expected)^2/expected. But which values are observed, and which are expected? And how do the marked values fit into this?

Question

We are using Chi Squares to understand if descrepancies in aniaml populations are random or significant.  On the developed land, 20 traps were set.  7 Road runners were caught, and two were marked.  On the Undeveloepd land, 20 traps were also set, but 11 Road Runners were caught and 1 was marked.  I know the formula for the chi square, x^2=sigma (observed-expected)^2/expected.  But which values are observed, and which are expected? And how do the marked values fit into this?