Light Weights

This problem is best tackled by using the formula given to you carefully. 

Christopher from Sale Grammar sent us his working here. He comments:

Using the values of 1956N and 1975N for the extremities of the earths surface we can see that the range of values would be 19N which equates to around 2kg. so, if a weightlifter was to do some weightlifting at the bottom of the Arctic, and then the top of Mount Chimborazo, they would feel a slight difference. However, when it comes to the main aim of the olympics, winning, it is clear that of course, everyone will be under the same stresses, so in terms of competition, everything will be fine. And there are other considerations at various altitudes too, such as air quality and density, and there are some serious considerations to be had at the bottom of the arctic. So in conclusion, yes, it would make a difference to the appeared strength of the weightlifter, but only by about 2kg.

Patrick from Otterborne included a table with his solution, showing the weight varying with altitude. How high would you have to go to lift 200kg?