It's not as simple as that Flecc. Russians are (or did, they now say site was hacked) saying around 10,000 soldiers dead and if as in other conflicts that would mean around double that number injured. Units with high levels of losses are withdrawn in attempts to limit demoralisation of remainder of troops... So its quite likely even tho losses are not at 20% (they couldn't operate at such levels) the resultant reduction in capacity to attack is probably way over that 20%..Accordung to reports all fronts are again static. Russia is facing massive losses, no matter how you assess it. Yes, Ukraine are also no doubt sustaining losses to both civilians and soldiers but with a conscript army at their call fighting for their homes the actual drop in capacity is minimal. Russians know all this, that's why they are attempting to demoralise public, blowing up hospitals and schools.
In many ways Russia has already lost this war. Trouble is they could well destroy Ukraine in an attempt to prove otherwise. But would razing another City to ground constitute victory..??? I doubt it.
From the start it always being fairly obvious Russia won't, can't just roll into Ukraine and take over. Putin was deluded to assume he could. Said it before, but Ukraine is size of France with 40 million inhabitants. 200,000 soldiers can not subdue that number of folk if they don't want to be subjugated, enslaved. Putin's reputation and reliance as such as Kadrov only stenghten Ukraine resolve.