Largely this is OK. I would put in a couple of articles, and, if you want to make it look "nicer", use a proper multiplication symbol and put spaces around it:
With an 80% sub-sampling rate, we have 0.8 × 0.8 = 64% shared points, but with a 20% rate only 4%. (I don't actually know what "80% sub-sampling rate" and "shared points" mean, but I am assuming