Rushbrooke inequality is a math problem that deals with adding numbers together. It has to do with something called "arranging numbers" which means putting them in order from smallest to biggest. For this problem, you have to arrange a group of numbers in such a way that the sums of the different groups are all the same. For example, if you have the numbers 1, 2, 3, 4, 5, and 6, you would need to organize them like this:
1 + 5 = 6
2 + 4 = 6
3 = 3
Since the sums of both groups are the same, 6, then the Rushbrooke inequality holds. To make sure it holds, you try different combinations until you find the right one. This can be tricky, but with some practice it becomes easier.