**The treatment arm showed a 20% risk reduction in progression free survival (HR=0.80, p = 0.05) in the entire population (n = 500). A subset of these patients (n = 400), showed a 30% risk reduction in progression free survival (HR=0.70, p = 0.005).**

I want to know as much as possible about the remaining 100 patients, but I'm shaky on the statistics. First, is it appropriate to use a weighted average to find the HR? If so, I'm assuming the calculation would just be: 0.80 = 0.70 (400/500) + x (100/500). Which would give an HR of 1.2 (meaning that the treatment arm was actually worse than the control). If this is right, is it possible to then determine the p value (given that I have none of the underlying data)?

Any help would be appreciated!