$400k, parents generation is retired with plenty of money. My point is more broadly that in a family where everyone can comfortably afford to live alone, living together can be massively more fun.
More like 5%. But the fact remains that "living alone" is considered aspirational in society, and that's not axiomatic. Plenty of American adults can afford to live alone, and do, but by pooling their resources with their parents, both can live on one property and have a much richer life together than living apart. My in-laws who live on the property sold their house to help us buy the property -- we couldn't have done it by ourselves, so we really had to break down some assumptions/default behaviors about financial independence which are fairly standard in the US.