0.1640625
= 1640625 / 10000000
So we can divide through 25, the top and bottom. Use your calculator
65625 / 400000
Divide through by 25 again
2625 / 16000
Divide through by 25 again
105 / 640
Divide through by 5
21 / 128
So that is the fraction in its simplest form.
It is just a simple fraction. It is not mixed.