How can you find the average temperature of a refrigerator or any fridge by using colligative properties?? I am doing a lab in school and i'm not sure how to approach or start this.

I know that you have to have two solutions where on one solution, you put a tremendous amount of salt and on the other solution, only a tiny bit. I think you put this in the fridge and find its freezing temperature?? Other than that.. please describe how you would do this!! Thanks.