Maybe this sounds a Little trivial.
I have a value and Over this value apply percentage (a), then over this result apply other percentage (b) Could say :
Value = 145760 a= 8% b= 40%
My actual calcs
R1= 145760 * (1-a)
R2= R1 * (1-b)
My question: there is a math rule that allow me to simplify the percentage to apply in one step.
My needs: I have a program that allow me to enter a single porcentaje then I need to get the percentage that matchs with my calcs with only one variable actually must do it by testing.
I am not sure if this is the thing you asked for but you could substitute R1 in R2 and get R2 = 145760 * (1-a) * (1-b) -> 145760 * c and your c is (1-a) * (1-b) other then that there probably won't be a way to simplify your task.