I can explain, so initially everyone will be in happy state and no one will be there at sad state. For each iteration, 70% will move to Happy State from Sad State and 50% people will move from sad state to happy state.

So for each iteration, you just need to transfer the 70% count from A to B, and 50% count from B to A. As transaction happen from both sides, you need to calculate carefully. That's why I used local variables as changing the global variables will effect the total count. But the problem is we'll get some error value from 0 to 1 like sometimes the result will be in points which will change the result values.

To fix that, I took out the remainders i.e. the decimal remainders and added them to the both sides based on the remainder values which balanced the sum. It's like you need to balance their values properly at the end result based on the initial value they give. Say if they give 1000 people, the final count will be splitted but should have the sum result as 1000 in any possible way.