new to this and stats overall so I hope i phrase this appropriately

one of our students created an experiment to look at the relationship between number of pieces of plastic and number of hermit crabs on a beach using quadrasts. They would like to first do a chi squared to look at plastic present (y/n) versus crabs present (y/n) but i'm having trouble explaining how to find the expected values.

1. would this make sense to do?

2. Could I ask someone experienced how you find the expected values?

much appreciated

thank you

sean