How do you find next 2 sets of numbers after 25 is to 64, 50 is to 32, 100 is to 16? What is the common ratio?

How do you find the next two sets of numbers for this? And what is the common ratio?How do you find next 2 sets of numbers after 25 is to 64, 50 is to 32, 100 is to 16? What is the common ratio?
First number doubles and second one halves so 200 to 8 and 400 to 4