I don't know the answer to this question but it may only require common sense: Let's say an apple on the surface of the earth weighs 0.25 Kg. Imagine the apple as the little earth and the whole earth on top of it. What is the weight of the earth with reference to that apple? I suspect the answer is 0.25 Kg also? If so, why? If not, then what is the correct answer and why?