Which one is good?
In Hungary, many people eat more than necessary.

In Hungary, many people eat more than that which is necessary.

Question

Which one is good?
In Hungary, many people eat more than necessary.

In Hungary, many people eat more than that which is necessary.

Answer

Both are correct. I think the second is overly complicated, so the first is better.

Answer

It depends on context with other sentences. As a stand alone I would go with the 1st sentence.

the second sentence I would also add a comma before which like : which.

Answer

These are both correct, they're just two different ways of expressing the same idea. The first one sounds more like normal, natural speech and the second is more formal, the kind you might see in an essay or a report.